[SurfaceFlinger] Refine expensive rendering trigger.

Previously we turned on expensive rendering when color mode is DISPLAY_P3
because wide color gamut implies V0_SCRGB dataspace with FP16 pixel format,
which can't be handled by hardware composer and it's also very expensive in GPU
composition. Now that DISPLAY_P3 color mode doesn't have this implication, we
should move the code to only trigger it if we hit GPU composition in DISPLAY_P3
color mode.

BUG: 114226412
Test: Build, flash and boot.
Test: Verify by modifying WCG to scRGB and checking GPU frequency.
Change-Id: Ia3d3c14574e9ac628497d2f9733e6dd84a2ed01d