vk_pipeline_cache: Add fallbacks for R8Srgb and B5G6R5 (#3264)

* vk_pipeline_cache: Add fallbacks for R8Srgb and B5G6R5

* blit_helper: Fix validation error

* renderer_vulkan: Emulate B5G6R5 with swizzle

src/video_core/amdgpu/pixel_format.h

@@ -248,6 +248,15 @@ constexpr CompMapping RemapSwizzle(const DataFormat format, const CompMapping sw
         result.a = swizzle.r;
         return result;
     }
+    case DataFormat::Format5_6_5: {
+        // Remap to a more supported component order.
+        CompMapping result;
+        result.r = swizzle.b;
+        result.g = swizzle.g;
+        result.b = swizzle.r;
+        result.a = swizzle.a;
+        return result;
+    }
     default:
         return swizzle;
     }