minigbm: don't advertise BGR24 as a render/texture target

minigbm: don't advertise BGR24 as a render/texture target

Mesa drivers can't use it, in general.

I'm leaving in Rockchip since I haven't gotten any reports
about this test failing on kevin-arcnext.

Fixes: abe44f ("minigbm: add support for BG24")

BUG=b:77876551, b:115564746
TEST=The following tests should pass on Eve/Grunt arc-next:

  android.hardware.nativehardware.cts.AHardwareBufferNativeTests#SingleLayer_ColorTest_GpuColorOutputAndSampledImage_R8G8B8_UNORM
  android.hardware.nativehardware.cts.AHardwareBufferNativeTests#SingleLayer_ColorTest_GpuColorOutputCpuRead_R8G8B8_UNORM
  android.hardware.nativehardware.cts.AHardwareBufferNativeTests#SingleLayer_ColorTest_GpuColorOutputIsRenderable_R8G8B8_UNORM
  android.hardware.nativehardware.cts.AHardwareBufferNativeTests#SingleLayer_ColorTest_GpuSampledImageCanBeSampled_R8G8B8_UNORM

Change-Id: Ic7aec07c89fdc21e0c8392238e833f7980062049
Reviewed-on: https://chromium-review.googlesource.com/1229439
Commit-Ready: Gurchetan Singh <gurchetansingh@chromium.org>
Tested-by: Gurchetan Singh <gurchetansingh@chromium.org>
Reviewed-by: Stéphane Marchesin <marcheu@chromium.org>