pinctrl: Always recurse into bcm folder

drivers/pinctrl/bcm/Makefile properly builds individual drivers based on
their respective Kconfig symbols. ARCH_BCM is currently a menuconfig
option from arch/arm/mach-bcm/Kconfig, which is fine, but prevents ARM64
platforms which do not have such menuconfig option from building their
pinctrl drivers, so let's get rid of that dependency.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Acked-by: Scott Branden <scott.branden@broadcom.com>
Acked-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>