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-ath79/Kconfig b/arch/mips/mach-ath79/Kconfig
index cd85d1b..2fa6285 100644
--- a/arch/mips/mach-ath79/Kconfig
+++ b/arch/mips/mach-ath79/Kconfig
@@ -8,7 +8,7 @@
 	bool
 	select MIPS_TUNE_24KC
 	select ROM_EXCEPTION_VECTORS
-	select SUPPORTS_BIG_ENDIAN
+	select SUPPORT_BIG_ENDIAN
 	select SUPPORTS_CPU_MIPS32_R1
 	select SUPPORTS_CPU_MIPS32_R2
 	help
@@ -17,7 +17,7 @@
 config SOC_AR934X
 	bool
 	select MIPS_TUNE_74KC
-	select SUPPORTS_BIG_ENDIAN
+	select SUPPORT_BIG_ENDIAN
 	select SUPPORTS_CPU_MIPS32_R1
 	select SUPPORTS_CPU_MIPS32_R2
 	select USB_EHCI_IS_TDI if USB_EHCI_HCD
@@ -28,7 +28,7 @@
 	bool
 	select MIPS_TUNE_24KC
 	select ROM_EXCEPTION_VECTORS
-	select SUPPORTS_BIG_ENDIAN
+	select SUPPORT_BIG_ENDIAN
 	select SUPPORTS_CPU_MIPS32_R1
 	select SUPPORTS_CPU_MIPS32_R2
 	help
@@ -37,7 +37,7 @@
 config SOC_QCA956X
 	bool
 	select MIPS_TUNE_74KC
-	select SUPPORTS_BIG_ENDIAN
+	select SUPPORT_BIG_ENDIAN
 	select SUPPORTS_CPU_MIPS32_R1
 	select SUPPORTS_CPU_MIPS32_R2
 	help