Correctly call setGpuStats() for ANGLE/system driver

In GraphicsEnvironment, correctly indicate if the loaded driver is ANGLE
or the system driver. This allows the 'dumpsys gpu' command to have the
correct value in the angleInUse field.

Bug: b/154955572
Test: adb shell dumpsys gpu
Test: atest CtsAngleIntegrationHostTestCases
Change-Id: I6db466b796e216367b0a220e432067b9ae6f485b