Always run color space math in full-float on the GPU (Part 2)

In https://reviews.skia.org/674396, we forced this code to run at full
precision in Ganesh (to fix Android HDR bugs). This CL applies the same
treatment to Graphite, and also cleans up an obsolete caps bit.

Change-Id: Iae1033f86ed8dda782bc32fc8ad994280a4ecac4
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/674398
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
8 files changed