drm/radeon: avoid moving the MC vram location (v2)

When setting up the memory controller, avoid moving
the vram location if possible. This should avoid
problems with hangs and corruption at boot especially
on UEFI systems due to invalid reads from the display
hardware when try and move the location of vram.

May fix:
https://bugs.freedesktop.org/show_bug.cgi?id=43655
https://bugs.freedesktop.org/show_bug.cgi?id=62976
https://bugs.freedesktop.org/show_bug.cgi?id=57567
et al.

v2: avoid moving crtc addresses as well

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org