arch: change default endian for microblaze

Fix the default for microblaze. Michal Simek mentioned default for
microblaze should be CPU_LITTLE_ENDIAN.

Fixes : commit 206d3642

 ("arch/microblaze: add choice for endianness
	and update Makefile")

Signed-off-by: Babu Moger <babu.moger@oracle.com>
Cc: Michal Simek <monstr@monstr.eu>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>