Skip flushing FPU/VFPU regs if none were allocated.

They're not used as often, so this usually saves time.  About 1% during
tests.
Cut time in EstimatePerVertexCost().

From profling, this cuts 4% time while lighting is enabled, and 14% while
disabled (on ARM.)  But maybe should just inline this...
Ensure stuff run on every prim are inlined.

These both get a ton of calls and show up on profiles.
Merge pull request #5770 from unknownbrackets/perf

Minor perf improvements for ARM