radeonsi: fix 109754
Bug 109754 reports a failure in util_blitter_generate_mipmap.
2 problems:
-
si_generate_mipmap
usesutil_blitter_generate_mipmap
without checking that util_blitter_generate_mipmap supports the requested format. That causes the assert from the bug report - after fixing the 1st issue, a second ones appears: when using threaded_context it's assumed that
pipe->generate_mipmap
cannot fails, which is false. So the second commit adds a fallback mechanism in this case.