[RenderEngine] Only compile Graphite if either Graphite flag is enabled

RE-Graphite will be *compiled* if either the graphite_renderengine
or force_compile_graphite_renderengine ready-only flag is enabled at
compile time (inclusive OR).

RE-Graphite can be compiled and *enabled* by:
1. setting just graphite_renderengine=true, or
2. setting both force_compile_graphite_renderengine=true and the
debug.renderengine.graphite system property to true.

Why RenderEngine needs a dep on libsurfaceflingerflags now:
libsurfaceflinger_common pulls in SF's FlagManager, which is layered on
top of the API that's autogenerated for SF's aconfig module,
libsurfaceflingerflags.
The COM_ANDROID_GRAPHICS_SURFACEFLINGER_FLAGS(...) macro is defined by
com_android_graphics_surfaceflinger_flags.h in that latter aconfig
module, and that header is not exported by the higher-level FlagManager
code.

Bug: b/293371537
Bug: b/331678326
Bug: b/341728634
Test: boot and bloaty (see b/331678326)
Flag: com.android.graphics.surfaceflinger.flags.graphite_renderengine
Change-Id: I9d0b15bda08430552716a9a1f7cd59d91ee7b9a6