MAINTAINERS: Add maintainers for amd-pinctrl driver

Adding Basavaraj and myself to the maintainers list for amd-pinctrl
driver.

Signed-off-by: Basavaraj Natikar <Basavaraj.Natikar@amd.com>
Signed-off-by: Shyam Sundar S K <Shyam-sundar.S-k@amd.com>
Link: https://lore.kernel.org/r/20210812115322.765379-1-Shyam-sundar.S-k@amd.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>