Support luminance-alpha GL format for YUVA planes

Bug: skia:10632
Change-Id: Ic91510b55644c15ee4eb5f96e7c35193b5ce49df
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/344761
Commit-Queue: Brian Salomon <bsalomon@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>
diff --git a/src/gpu/SkGr.cpp b/src/gpu/SkGr.cpp
index d08b4f0..39e4c48 100644
--- a/src/gpu/SkGr.cpp
+++ b/src/gpu/SkGr.cpp
@@ -176,6 +176,7 @@
         case GrColorType::kAlpha_8:
         case GrColorType::kAlpha_8xxx:
         case GrColorType::kGray_8:
+        case GrColorType::kGrayAlpha_88:
         case GrColorType::kGray_8xxx:
         case GrColorType::kR_8:
         case GrColorType::kRG_88: