drm/radeon: always program the MC on startup

commit 6fab3febf6d949b0a12b1e4e73db38e4a177a79e upstream.

For r6xx+ asics.  This mirrors the behavior of pre-r6xx
asics.  We need to program the MC even if something
else in startup() fails.  Failure to do so results in
an unusable GPU.

Based on a fix from: Mark Kettenis <kettenis@openbsd.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
[bwh: Backported to 3.2: adjust context, drop changes to cik.c and si.c]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>