Move srgb enable flags to GrProcessorSet from pipelinebuilder

BUG=skia:

Change-Id: I533d032a8019980b3870d432ada59bac805d7c36
Reviewed-on: https://skia-review.googlesource.com/7268
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
5 files changed