drm/amd/pm/ci: Don't disable MCLK DPM on Bonaire 0x6658 (R7 260X)

drm/amd/pm/ci: Don't disable MCLK DPM on Bonaire 0x6658 (R7 260X)

The old radeon driver has a documented workaround in ci_dpm.c
which claims that Bonaire 0x6658 with old memory controller
firmware is unstable with MCLK DPM, so as a precaution I
disabled MCLK DPM on this ASIC in amdgpu.

Note that the old MC firmware is not actually used with
amdgpu, but in theory it's possible that the VBIOS sets
up the ASIC with an old MC firmware that is already running
when amdgpu initializes (in which case amdgpu doesn't
load its own firmware).

What I expected to happen is that the GPU would simply use
its maximum memory clock, and indeed this is what seemed
to happen according to amdgpu_pm_info which reads the
current MCLK value from the SMU.
However, some users reported a huge perf regression
and upon a closer look it seems that the GPU seems to
not actually use the highest MCLK value, despite the SMU
reporting that it does.

Let's not disable MCLK DPM on Bonaire 0x6658 (R7 260X).

Keep MCLK DPM disabled on R9 M380 in the 2015 iMac
because that still hangs if we enable it.

Fixes: 9851f29cb06c ("drm/amd/pm/ci: Disable MCLK DPM on problematic CI ASICs")
Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit d34acad064ee7d82bd18f5d87592c422d4d323ac)
Cc: stable@vger.kernel.org