Revert "drm/radeon: disable runtime pm on PX laptops without dGPU power control"

This reverts commit e64c952efb8e0c15ae82cec8e455ab4910690ef1.

ATPX is the ACPI method for controlling AMD PowerXpress laptops.
There are flags to indicate which methods are supported.  If
the dGPU power down flag is not supported, the driver needs to
implement the dGPU power down manually.  We had previously
always forced the driver to assume the ATPX dGPU power down
was present, but this causes problems on boards where it is
not, leading to GPU hangs when attempting to power down the
dGPU.  Manual dGPU power down is not currently supported in
the Linux driver.  Some laptops indicate that the ATPX
dGPU power down method is not present, but it actually
apparently is.  I'm not sure if this is a bios bug and it should
be set or if there is a reason it was unset and the method should
not be used.  This is not an issue on other OSes since both the
ATPX and the manual driver power down methods are supported.

This is apparently fairly widespread, so just revert for now.

bugs:
https://bugzilla.kernel.org/show_bug.cgi?id=115321
https://bugzilla.kernel.org/show_bug.cgi?id=116581
https://bugzilla.kernel.org/show_bug.cgi?id=116251

Cc: stable@vger.kernel.org