mt76: connac: fix unresolved symbols when CONFIG_PM is unset

mt76_connac_mcu_reg_* functions are always needed by connac based drivers

Fixes: 87f9bf24

 ("mt76: connac: move mcu reg access utility routines in mt76_connac_lib module")
Signed-off-by: Felix Fietkau <nbd@nbd.name>