Replace VPXMIN+VPXMAX combos with clamp or fclamp

This change is similar to the change in libaom:
466bfbce9d Replace AOMMIN+AOMMAX combos with clamp or fclamp

VPXMIN and VPXMAX are macros, so their arguments are evaluated twice. It
is especially bad if VPXMIN and VPXMAX are used together to clamp a
value to a range. Replace that combination with the clamp() or fclamp()
inline function.

Change-Id: I694f3da444bfdac95e902dd03b5a4f0c736ea8df
8 files changed