Force HALs to explicitly enable legacy method for clearing buffer caches

Some HAL implementations can't support setLayerBuffer multiple times to
clear the per-layer buffer caches. Therefore, default this behavior to
disabled, and allow HALs to explcitily enable this behavior to obtain
the necessary memory savings.

Test: play videos with both true and false on both HIDL and AIDL
Bug: 285561686
Merged-In: I928cef25e35cfc5337db4ceb8581bf5926b4fbe3
Change-Id: I928cef25e35cfc5337db4ceb8581bf5926b4fbe3