riscv: Remove CONFIG_PHYS_RAM_BASE_FIXED

Make the physical RAM base address available for all kernels, not only
XIP kernels as it will allow to simplify address conversions macros.
Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>

arch/riscv/Kconfig

@@ -490,13 +490,8 @@ config STACKPROTECTOR_PER_TASK
 	def_bool y
 	depends on STACKPROTECTOR && CC_HAVE_STACKPROTECTOR_TLS
 
-config PHYS_RAM_BASE_FIXED
-	bool "Explicitly specified physical RAM address"
-	default n
-
 config PHYS_RAM_BASE
 	hex "Platform Physical RAM address"
-	depends on PHYS_RAM_BASE_FIXED
 	default "0x80000000"
 	help
 	  This is the physical address of RAM in the system. It has to be
@@ -509,7 +504,6 @@ config XIP_KERNEL
 	# This prevents XIP from being enabled by all{yes,mod}config, which
 	# fail to build since XIP doesn't support large kernels.
 	depends on !COMPILE_TEST
-	select PHYS_RAM_BASE_FIXED
 	help
 	  Execute-In-Place allows the kernel to run from non-volatile storage
 	  directly addressable by the CPU, such as NOR flash. This saves RAM