ARM: dts: am33xx: Added AM33XX_PADCONF macro

AM33XX_PADCONF takes three instead of two parameters, to make
future changes to #pinctrl-cells easier.

For old boards which are not mainlined, we left the AM33XX_IOPAD
macro.

Signed-off-by: Christina Quast <cquast@hanoverdisplays.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>