pinctrl/amd: Fix build dependency on pinmux code

The commit 79d2c8be ("pinctrl/amd: save pin registers over
suspend/resume") caused the following compilation errors:

drivers/pinctrl/pinctrl-amd.c: In function ‘amd_gpio_should_save’:
drivers/pinctrl/pinctrl-amd.c:741:8: error: ‘const struct pin_desc’ has no member named ‘mux_owner’
  if (pd->mux_owner || pd->gpio_owner ||
        ^
drivers/pinctrl/pinctrl-amd.c:741:25: error: ‘const struct pin_desc’ has no member named ‘gpio_owner’
  if (pd->mux_owner || pd->gpio_owner ||

We need to enable CONFIG_PINMUX for this driver as well.

Cc: stable@vger.kernel.org
Fixes: 79d2c8be ("pinctrl/amd: save pin registers over suspend/resume")
Signed-off-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>