ActivityManager: Memoize graphics acceleration check

Account for devices without hardware rendering support

Original commit message and code modified to be cleaner and clearer.

Patchset 2 & 3 : Whitespace cleanup

Patchset 4 : Meet guidelines here:
http://aokp.co/learn/aokp-code-style-guidelines

Change-Id: Ib400d85a261d9c5d0fd5770d6cda5f61832cba6b