dt-bindings: pinctrl: Convert TI DA850 pupd to DT schema

Convert the Texas Instruments DA850/OMAP-L138/AM18x pullup/down
controller bindings to DT schema.

Signed-off-by: Eduard Bostina <egbostina@gmail.com>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Linus Walleij <linusw@kernel.org>