evas/software_generic: Round up merged rect to tile size

evas/software_generic: Round up merged rect to tile size

Summary:
For some drivers, there is a limitation for partial rects that only
multiples of tile size width/height are allowed.
Currently, rects are merged based on the current rotation, so when
the rects are calculated based on 0 rotation it does not meet the above
requirement.
Add a rect rounding up routine after _merge_rects such that the rect
is rounded up to tile size based on 0 rotation.

Change-Id: I0ac0208e383332158dc7c3fa9fa5012e37bcf797