Kconfig: Unify endian support option

Move SUPPORT_BIG_ENDIAN, SUPPORT_LITTLE_ENDIAN to top-level
arch Kconfig and let architectures select them as necessary.

Remove if guard for Endianness selection choice so we can
have one of SYS_BIG_ENDIAN, SYS_LITTLE_ENDIAN config symbol
defined even on single endian system.

Default endian to SYS_BIG_ENDIAN for MIPS || MICROBLAZE
and LITTLE_ENDIAN for the rest to retain old config
behaviour.

Note: PPC, SH, Xtensa are technically bi-endian, but I
checked compiled u-boot image with readelf, U-Boot currently
only support little endian for SH and Xtensa, Big Endian for
PPC.

Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
diff --git a/arch/mips/mach-pic32/Kconfig b/arch/mips/mach-pic32/Kconfig
index 2afa972..52d2eec 100644
--- a/arch/mips/mach-pic32/Kconfig
+++ b/arch/mips/mach-pic32/Kconfig
@@ -13,7 +13,7 @@
 	select ROM_EXCEPTION_VECTORS
 	select SUPPORTS_CPU_MIPS32_R1
 	select SUPPORTS_CPU_MIPS32_R2
-	select SUPPORTS_LITTLE_ENDIAN
+	select SUPPORT_LITTLE_ENDIAN
 	select SYS_MIPS_CACHE_INIT_RAM_LOAD
 	help
 	  This supports Microchip PIC32MZ[DA] family of microcontrollers.