Revert "Remove a usage of GrPixelConfig in SkGpuBlurUtils::GaussianBlur"

This reverts commit f580721e1118407ca9f454d83eb52cbfe9ed2c3a.

Reason for revert: maybe angle bots

Original change's description:
> Remove a usage of GrPixelConfig in SkGpuBlurUtils::GaussianBlur
> 
> Bug: skia:6718
> Change-Id: Ia8a96cf6907ffaafd989f1e5bb1443d1ef51b9e6
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/242142
> Reviewed-by: Brian Salomon <bsalomon@google.com>
> Commit-Queue: Robert Phillips <robertphillips@google.com>

TBR=bsalomon@google.com,robertphillips@google.com

Change-Id: Ifcd22699ed64c7020c5d33781062c267595e246e
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: skia:6718
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/242820
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
18 files changed