On recent Broadcom chipsets PMU is present as separated core and it
can't be accessed using ChipCommon anymore as it fails with e.g.:
[   18.198412] Unhandled fault: imprecise external abort (0x1406) at 0xb6da200f

Add a new helper function that will return a proper core that should be
used for accessing PMU registers.
Signed-off-by: NRafał Miłecki <zajec5@gmail.com>
Signed-off-by: NKalle Valo <kvalo@codeaurora.org>