Remove FlagManager's dependence on librenderengine

libsurfaceflinger_common_defaults previously depended on
librenderengine, but only for a #define in a header file. This prevents
librenderengine from using the FlagManager.

Add a new library for renderengine includes, so FlagManager can access
the define without depending on the entire library.

Bug: 305445199
Bug: 255921628
Test: make
Change-Id: Ibee8581cfc0ac8c4817725bbf1fb12efc744c4c1