malloc: Use malloc simple before malloc is fully initialized in memalign()

Follow implementation in mALLOc(). Check GD_FLG_FULL_MALLOC_INIT flag and use
malloc_simple if GD_FLG_FULL_MALLOC_INIT is unset. Adjust the malloc bytes
to align with the requested alignment.

The original memalign() function will access mchunkptr struct to adjust the
alignment if there is misalignment happen, but mchunkptr struct is not being
initialized before full malloc is initialized. This cause the system crash.

Signed-off-by: Ley Foon Tan <ley.foon.tan@intel.com>
Reviewed-by: Marek Vasut <marek.vasut@gmail.com>