bcma: support BCM53573 series of wireless SoCs

BCM53573 seems to be the first series of Northstar family with wireless
on the chip. The base models are BCM53573-s (A0, A1) and there is also
BCM47189B0 which seems to be some small modification.

The only problem with these chipsets seems to be watchdog. It's totally
unavailable on 53573A0 / 53573A1 and preferable PMU watchdog is broken
on 53573B0 / 53573B1.

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