drm/amdgpu: disable runpm if we are the primary adapter

If we are the primary adapter (i.e., the one used by the firwmare
framebuffer), disable runtime pm.  This fixes a regression caused
by commit 55285e21 which results in the displays waking up
shortly after they go to sleep due to the device coming out of
runtime suspend and sending a hotplug uevent.

v2: squash in reworked fix from Evan

Fixes: 55285e21 ("fbdev/efifb: Release PCI device's runtime PM ref during FB destroy")
Bug: https://bugzilla.kernel.org/show_bug.cgi?id=215203
Bug: https://gitlab.freedesktop.org/drm/amd/-/issues/1840


Signed-off-by: Alex Deucher <alexander.deucher@amd.com>