Revert "Revert "ActivityManager: Rejigger HighEndGfx: only propget/stringcomp and resget once (in isHighEnd, rather than constructor)""

Corrected inverted conditions.
That variable name NOPE threw me off. :-P
if NOPE was true, _isHighEndGfx was false.
!config_avoidGfxAccel && !isLowRamDeviceStatic should be a close enough approximation of devices having GPUs. It's sufficient for every ROM except for wherever that line came from.

This reverts commit f3675d5c14d5bee468c9a2a7385d76e8c7e180a7.

Change-Id: I13f6db99041df4b92a376eb2d7ec0cbc089ee957