SF: Simplify dumpsys flag parsing

This CL removes sequential parsing for dumpsys flags, which was order-
dependent and boilerplate-heavy.

Note that flags cannot be combined for simplicity.

Bug: None
Test: dumpsys SurfaceFlinger [--FLAG [ARGS...]]
Change-Id: Id305ffee464c6cad4f228c7a7f603c33a2978d66