Optimize bootanimation and reduce jitters

Summary:
Optimize the Bootanimation and always keep three buffers ready.

Credit @AndroidRul3z and @Cyanogen respectively.

Test Plan: Test and merge

Reviewers: synergy, randall.rushing, donald.munn, anders3408, raymanfx

Reviewed By: raymanfx

Differential Revision: http://review.codefirex.com/D516