Re-enable dmabuf mmap in Chromecast builds

Original graphical artifacts no longer reproduce.

Bug: b/171980418
Test: Check for artifacts during boot.
Change-Id: Ie1501c903d4bc63f065de699c0dd4db2d6c206af
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2572708Reviewed-by: Daniele Castagna <dcastagna@chromium.org>
Commit-Queue: Daniel Nicoara <dnicoara@chromium.org>
Cr-Commit-Position: refs/heads/master@{#834310}

ui/gfx/linux/client_native_pixmap_dmabuf.cc

@@ -94,16 +94,6 @@ ClientNativePixmapDmaBuf::PlaneInfo::~PlaneInfo() {
 bool ClientNativePixmapDmaBuf::IsConfigurationSupported(
     gfx::BufferFormat format,
     gfx::BufferUsage usage) {
-#if BUILDFLAG(IS_CHROMECAST)
-  switch (usage) {
-    case gfx::BufferUsage::GPU_READ_CPU_READ_WRITE:
-      // TODO(spang): Fix b/121148905 and turn these back on.
-      return false;
-    default:
-      break;
-  }
-#endif
-
   bool disable_yuv_biplanar = true;
 #if BUILDFLAG(IS_CHROMEOS_ASH) || BUILDFLAG(IS_CHROMECAST)
   // IsConfigurationSupported(SCANOUT_CPU_READ_WRITE) is used by the renderer