nios2: remove redundant 'default n' from Kconfig-s

'default n' is the default value for any bool or tristate Kconfig
setting so there is no need to write it explicitly.

Also since commit f467c564 ("kconfig: only write '# CONFIG_FOO
is not set' for visible symbols") the Kconfig behavior is the same
regardless of 'default n' being present or not:

    ...
    One side effect of (and the main motivation for) this change is making
    the following two definitions behave exactly the same:

        config FOO
                bool

        config FOO
                bool
                default n

    With this change, neither of these will generate a
    '# CONFIG_FOO is not set' line (assuming FOO isn't selected/implied).
    That might make it clearer to people that a bare 'default n' is
    redundant.
    ...
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Signed-off-by: Ley Foon Tan <ley.foon.tan@intel.com>

arch/nios2/Kconfig

@@ -122,7 +122,6 @@ config NIOS2_CMDLINE_IGNORE_DTB
 
 config NIOS2_PASS_CMDLINE
 	bool "Passed kernel command line from u-boot"
-	default n
 	help
 	  Use bootargs env variable from u-boot for kernel command line.
 	  will override "Default kernel command string".

arch/nios2/platform/Kconfig.platform

@@ -17,7 +17,6 @@ comment "Device tree"
 
 config NIOS2_DTB_AT_PHYS_ADDR
 	bool "DTB at physical address"
-	default n
 	help
 	  When enabled you can select a physical address to load the dtb from.
 	  Normally this address is passed by a bootloader such as u-boot but
@@ -37,7 +36,6 @@ config NIOS2_DTB_PHYS_ADDR
 
 config NIOS2_DTB_SOURCE_BOOL
 	bool "Compile and link device tree into kernel image"
-	default n
 	help
 	  This allows you to specify a dts (device tree source) file
 	  which will be compiled and linked into the kernel image.
@@ -62,21 +60,18 @@ config NIOS2_ARCH_REVISION
 
 config NIOS2_HW_MUL_SUPPORT
 	bool "Enable MUL instruction"
-	default n
 	help
 	  Set to true if you configured the Nios II to include the MUL
 	  instruction.  This will enable the -mhw-mul compiler flag.
 
 config NIOS2_HW_MULX_SUPPORT
 	bool "Enable MULX instruction"
-	default n
 	help
 	  Set to true if you configured the Nios II to include the MULX
 	  instruction.  Enables the -mhw-mulx compiler flag.
 
 config NIOS2_HW_DIV_SUPPORT
 	bool "Enable DIV instruction"
-	default n
 	help
 	  Set to true if you configured the Nios II to include the DIV
 	  instruction.  Enables the -mhw-div compiler flag.
@@ -84,7 +79,6 @@ config NIOS2_HW_DIV_SUPPORT
 config NIOS2_BMX_SUPPORT
 	bool "Enable BMX instructions"
 	depends on NIOS2_ARCH_REVISION = 2
-	default n
 	help
 	  Set to true if you configured the Nios II R2 to include
 	  the BMX Bit Manipulation Extension instructions. Enables
@@ -93,7 +87,6 @@ config NIOS2_BMX_SUPPORT
 config NIOS2_CDX_SUPPORT
 	bool "Enable CDX instructions"
 	depends on NIOS2_ARCH_REVISION = 2
-	default n
 	help
 	  Set to true if you configured the Nios II R2 to include
 	  the CDX Bit Manipulation Extension instructions. Enables
@@ -101,13 +94,11 @@ config NIOS2_CDX_SUPPORT
 
 config NIOS2_FPU_SUPPORT
 	bool "Custom floating point instr support"
-	default n
 	help
 	  Enables the -mcustom-fpu-cfg=60-1 compiler flag.
 
 config NIOS2_CI_SWAB_SUPPORT
 	bool "Byteswap custom instruction"
-	default n
 	help
 	  Use the byteswap (endian converter) Nios II custom instruction provided
 	  by Altera and which can be enabled in QSYS builder. This accelerates