dt-bindings: pinctrl: k3: Introduce pinmux definitions

The dt-bindings header for TI K3 AM6 SoCs define a set of macros for
defining pinmux configs in human readable form, instead of raw-coded
hex values.

Signed-off-by: Vignesh R <vigneshr@ti.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Nishanth Menon <nm@ti.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Tero Kristo <t-kristo@ti.com>