Move SkYUVAIndex and SkImageSourceChannel to SkImageInfoPriv.h until used in public API

Change-Id: Ib75be2b6e9eb9b80f1f9e738bc8e3300ddc08f22
Reviewed-on: https://skia-review.googlesource.com/129927
Commit-Queue: Brian Salomon <bsalomon@google.com>
Reviewed-by: Cary Clark <caryclark@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>
3 files changed