revert: 'bootanimation: allow using RGB565 instead of ARGB8888'

RGB565 uses considerably less memory, and together with texture
cache, it allows us to offer a really smooth bootanimation on
not so powerful devices.

Change-Id: I9da8fd7e6a587b5895519dd0983ec9b8f676771b (reverse-merged from commit 45c1b873352b632c32cd51ea21c1e90f066770e9)