gpio: Add proper dependency on ZYNQMP_FIRMWARE

ZYNQMP_FIRMWARE can be disabled and driver depends on it that's why record
this dependency via Kconfig.

Signed-off-by: Michal Simek <michal.simek@amd.com>
Link: https://lore.kernel.org/r/c3ca38fbb2f4e6948a5ef95b369015de96259709.1717685091.git.michal.simek@amd.com