ARM: dts: keystone: Header file for pinctrl constants

The pinctrl IP used in some of the Keystone 2 devices differ vs other
TI SoCs. Therefore, create a Keystone specific pinctrl header.

Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
Signed-off-by: Franklin S Cooper Jr <fcooper@ti.com>
Signed-off-by: Tero Kristo <t-kristo@ti.com>
Signed-off-by: Dave Gerlach <d-gerlach@ti.com>
Signed-off-by: Santosh Shilimkar <ssantosh@kernel.org>