fs: Make efivarfs a pseudo filesystem, built by default with EFI

efivars is currently enabled under MISC_FILESYSTEMS, which is decribed
as "such as filesystems that came from other operating systems".
In reality, it is a pseudo filesystem, providing access to the kernel
UEFI variable interface.

Since this is the preferred interface for accessing UEFI variables, over
the legacy efivars interface, also build it by default as a module if
CONFIG_EFI.
Signed-off-by: Leif Lindholm <leif.lindholm@linaro.org>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>

fs/Kconfig

@@ -165,6 +165,7 @@ config HUGETLB_PAGE
 	def_bool HUGETLBFS
 
 source "fs/configfs/Kconfig"
+source "fs/efivarfs/Kconfig"
 
 endmenu
 
@@ -209,7 +210,6 @@ source "fs/sysv/Kconfig"
 source "fs/ufs/Kconfig"
 source "fs/exofs/Kconfig"
 source "fs/f2fs/Kconfig"
-source "fs/efivarfs/Kconfig"
 
 endif # MISC_FILESYSTEMS
 

fs/efivarfs/Kconfig

 config EFIVAR_FS
 	tristate "EFI Variable filesystem"
 	depends on EFI
+	default m
 	help
 	  efivarfs is a replacement filesystem for the old EFI
 	  variable support via sysfs, as it doesn't suffer from the