arm64: dts: imx8mp: Add pinctrl config definitions

arm64: dts: imx8mp: Add pinctrl config definitions

Currently to configure each IOMUXC_SW_PAD_CTL_PAD the raw value of this
register is written in the dts, these values are not obvious. Add defines
which describe the fields of this register which can be or-ed together to
produce readable settings.

Reviewed-by: Frank Li <Frank.Li@nxp.com>
Acked-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Maud Spierings <maudspierings@gocontroll.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>