bcma: use _PMU_ in all names of PMU registers

PMU (Power Management Unit) seems to be a separated piece of hardware,
just accessed using ChipCommon core registers. In recent Broadcom
chipsets PMU is not bounded to CC but available as separated core.

To make code cleaner & easier to review (for a correct R/W access) use
clearer names.

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>