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

target/product/mainline_system.mk

@@ -88,6 +88,11 @@ PRODUCT_PACKAGES_DEBUG += \
     tinypcminfo \
     update_engine_client \
 
+# Enable stats logging in LMKD
+TARGET_LMKD_STATS_LOG := true
+PRODUCT_SYSTEM_DEFAULT_PROPERTIES += \
+    ro.lmk.log_stats=true
+
 # Enable dynamic partition size
 PRODUCT_USE_DYNAMIC_PARTITION_SIZE := true