drivers: gpio: rgpio: use default pad config value for SCMI platform

If the platform uses SCMI pinctrl driver, pinctrl regitster can't accessed
by CPU Core directly, and currently SCMI pinctrl driver has no API to read
back the register value, so use default pad config value for GPIO pad
configuration, and in theory we could use a fixed pad config value in this
driver as each new GPIO configuration has no relation with previous
configuration.

Signed-off-by: Jiafei Pan <Jiafei.Pan@nxp.com>