pinctrl: microchip-sgpio: add missing select REGMAP_MMIO

pinctrl: microchip-sgpio: add missing select REGMAP_MMIO

The driver calls ocelot_regmap_from_resource() via <linux/mfd/ocelot.h>,
which internally uses devm_regmap_init_mmio() and requires REGMAP_MMIO.
The Kconfig entry does not select REGMAP_MMIO, causing a build failure
when no other driver in the config happens to pull in REGMAP_MMIO:

  include/linux/mfd/ocelot.h:34:24: error: implicit declaration of function 'devm_regmap_init_mmio'

Found by randconfig testing on arm64; tinyconfig reproducer below.

Fixes: 2afbbab45c26 ("pinctrl: microchip-sgpio: update to support regmap")
Cc: stable@vger.kernel.org
Signed-off-by: Benjamin Boortz <bennib@mailbox.org>
Reviewed-by: Andy Shevchenko <andy@kernel.org>
Signed-off-by: Linus Walleij <linusw@kernel.org>