drm/radeon: fix PM on non-vram cards.

PM attemps to unmap objects that aren't actually mapped into userspace ever,
so just don't bother unmapping them at this point, since all you are doing
is nothing. We should be making sure all access to these objects are locked in
kernel space instead. In theory the VRAM gart table is already done, and both
the shaders and stolen vga memory blocks are never accessed at runtime.

fixes: https://bugzilla.kernel.org/show_bug.cgi?id=16127



Reported-by: Jure Repnic <jlp.bugs@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>