MIPS: kconfig: add options for endianess select

Add new Kconfig option to let the user select the targets
endianess. Each target have to select SUPPORTS_BIG_ENDIAN
and/or SUPPORTS_LITTLE_ENDIAN to indicate which endianess
is supported.

Signed-off-by: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
diff --git a/configs/vct_platinumavc_onenand_small_defconfig b/configs/vct_platinumavc_onenand_small_defconfig
index 31b4c9a..f254ab6 100644
--- a/configs/vct_platinumavc_onenand_small_defconfig
+++ b/configs/vct_platinumavc_onenand_small_defconfig
@@ -1,4 +1,5 @@
 CONFIG_SYS_EXTRA_OPTIONS="VCT_PLATINUMAVC,VCT_ONENAND,VCT_SMALL_IMAGE"
 CONFIG_MIPS=y
 CONFIG_TARGET_VCT=y
+CONFIG_SYS_BIG_ENDIAN=y
 # CONFIG_CMD_CRC32 is not set