gpio_smartbond: Fix port_set_masked_raw

Writing directly to Px_DATA_REG modifies pins which are not
indicated by mask, causing gpio_basic_api test to fail.

Use Px_SET_DATA_REG and Px_RESET_DATA_REG to modify only
pins indicated by mask.

Signed-off-by: Ioannis Damigos <ioannis.damigos.uj@renesas.com>