Add cmdline switch --skip-film-grain to aomdec
Add cmdline switch --skip-film-grain to aomdec

This commit adds a commandline switch "--skip-film-grain" to aomdec,
which allows decoder to output decoded video either with film grain
applied or without film grain applied.

BUG=aomedia:2126

Change-Id: I3f98dbb83e14343de9bd6c7230bfe736e51985f1

GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom