pinctrl: meson: a4: Add input enable pin configuration

Add support for PIN_CONFIG_INPUT_ENABLE in the Amlogic A4 pinctrl
driver.

Use the existing output enable control to configure the input enable
state, since the hardware uses the same control with inverse semantics.

Also update PIN_CONFIG_OUTPUT_ENABLE handling to return the actual
output enable state instead of treating any non-zero value as enabled.

Signed-off-by: Xianwei Zhao <xianwei.zhao@amlogic.com>
Signed-off-by: Linus Walleij <linusw@kernel.org>