pinctrl: bcm2835: Allow building driver as a module

Update the pinctrl-bcm2835 driver to support being built as as a module
by converting it to a module_platform_driver() with the appropriate
module license, authors and description.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Nicolas Saenz Julienne <nsaenz@kernel.org>
Link: https://lore.kernel.org/r/20211019221127.1953001-1-f.fainelli@gmail.com


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>