eina_mempool: change default memory alignment from 2 to 4

eina_mempool: change default memory alignment from 2 to 4

This patch is still in review.
https://phab.enlightenment.org/D9520/

If the patch would be modified while reviewing, this patch
should be reverted and the reviewed one needs to be updated.

[Summary]
SIGBUS error occurs on ARM devices. ELM_LAYOUT_MIXIN inherited class data size
is not a multiple of 4, because sizeof(Elm_Layout_Data) is 1 and
eina_mempool_alignof return 2 with size less than 4 which means data_offset
is a * m + 2.

@tizen_fix

Change-Id: I2c25d14def886f4d2ccb0b775ea540c9d41b8c9e