clk: bcm: Allow CLK_BCM2835 for ARCH_BRCMSTB

ARCH_BRCMSTB needs to use the BCM2835 clock driver for chips like
BCM7211 which adopted that clock controller, make that possible and the
driver default to be enabled for ARCH_BRCMSTB.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>