pinctrl: bcm: Add STB family pin controller driver

pinctrl: bcm: Add STB family pin controller driver

This driver provide pin muxing and configuration functionality
for BCM2712 SoC used by RPi5. According to [1] this chip is an
instance of the one used in Broadcom STB  product line.

[1] https://lore.kernel.org/lkml/f6601f73-cb22-4ba3-88c5-241be8421fc3@broadcom.com/

Cc: Jonathan Bell <jonathan@raspberrypi.com>
Cc: Phil Elwell <phil@raspberrypi.com>
Signed-off-by: Ivan T. Ivanov <iivanov@suse.de>
Reviewed-by: Phil Elwell <phil@raspberrypi.com>
Signed-off-by: Andrea della Porta <andrea.porta@suse.com>
[linusw: Enable also for ARCH_BCM2835]
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>