drm/radeon: fix runpm handling on APUs (v4)

Don't try and runtime suspend the APU in PX systems.  We
only want to power down the dGPU.

v2: fix harder
v3: fix stupid typo
v4: consolidate runpm enablement to a single flag

bugs:
https://bugs.freedesktop.org/show_bug.cgi?id=75127
https://bugzilla.kernel.org/show_bug.cgi?id=72701

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
diff --git a/drivers/gpu/drm/radeon/radeon.h b/drivers/gpu/drm/radeon/radeon.h
index f21db7a..7014bdd 100644
--- a/drivers/gpu/drm/radeon/radeon.h
+++ b/drivers/gpu/drm/radeon/radeon.h
@@ -2321,6 +2321,7 @@
 	bool have_disp_power_ref;
 };
 
+bool radeon_is_px(struct drm_device *dev);
 int radeon_device_init(struct radeon_device *rdev,
 		       struct drm_device *ddev,
 		       struct pci_dev *pdev,