mt76: mt7921: do not always disable fw runtime-pm

After commit 'd430dffb ("mt76: mt7921: fix a possible race
enabling/disabling runtime-pm")', runtime-pm is always disabled in the
fw even if the user requests to enable it toggling debugfs node since
mt7921_pm_interface_iter routine will use pm->enable to configure the fw.
Fix the issue moving enable variable configuration before running
mt7921_pm_interface_iter routine.

Fixes: d430dffb ("mt76: mt7921: fix a possible race enabling/disabling runtime-pm")
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Felix Fietkau <nbd@nbd.name>