Add two compile flags for mainline

- LMKD_LOG_STATS being false is a disk-saving flag not suitable
  for mainline
- USE_HWC2 should likely be cleaned up, but toggles some timing
  behavior in libhwui

Bug: 80410283
Test: build mainline_system_arm64
Change-Id: I8a1be50bd2cc48405656cd1daad8e8a1ca555871