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 <stefan.wahren@i2se.com>
Reviewed-by: Eric Anholt <eric@anholt.net>