UAPI header should not use Kconfig items

Use __BIG_ENDIAN__ defined as a compiler intrinsic
Signed-off-by: Noam Camus <noamc@ezchip.com>
[vgupta: fix changelog]
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>