Add GL Caps for Radeon Pro Vega

The Pro Vega is used in the iMac Pro, and has the following
string:
"AMD Radeon Pro Vega 56 OpenGL Engine"

Make it behave like kAMDRadeonHD7xxx_GrGLRenderer.

Change-Id: I3eb60a56e0d10df6d5deab18302514d0ae3b2a56
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/251116
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Herb Derby <herb@google.com>
3 files changed