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

Broke status bar transparency. There are also devices that don't have GPU, so restore check.

This reverts commit de5531d256f79e2a3d7ee7eb979bf1be7bc9dd19.

Change-Id: I39f6eac02e3e2fbb5614886591968642d17a74cc