pinctrl: single: add support for pinctrl-single, pins when #pinctrl-cells = 2

Changes to the am33xx device (33e9021a) trees have been merged in from
the upstream linux kernel which now means the device tree uses the new
pins format (as of 5.10) where the confinguration can be stores as a
separate configuration value and pin mux mode which are then OR'd
together.

This patch adds support for the new format to u-boot so that
pinctrl-cells is now respected when reading in pinctrl-single,pins
Signed-off-by: Anthony Bagwell <anthony.bagwell@hivehome.com>