drm_hwcomposer: Remove hardcoded PAGE_SIZE usage in gralloc_helper am: b9ae59025f am: 654d079921

Original change: https://android-review.googlesource.com/c/platform/external/drm_hwcomposer/+/3017877

Change-Id: I7f5652f4f23ec33a0be407111dfbe3b9ff299a98
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>