soc: bcm: Make PM driver default for BCM2835

Since commit 52a4adbaebcc ("ARM: bcm283x: Switch V3D over to using the
PM driver instead of firmware.") VC4 on BCM2835 requires the power driver.

Otherwise the driver won't probe and HDMI output stays black:
vc4_v3d 20c00000.v3d: ignoring dependency for device, assuming no driver

Signed-off-by: Stefan Wahren <[e-mail]>
Reviewed-by: Eric Anholt <[e-mail]>

drivers/soc/bcm/Kconfig

···
 config BCM2835_POWER
 	bool "BCM2835 power domain driver"
 	depends on ARCH_BCM2835 || (COMPILE_TEST && OF)
+	default y if ARCH_BCM2835
 	select PM_GENERIC_DOMAINS if PM
 	select RESET_CONTROLLER
 	help