ARM: dts: koelsch: Configure pull-up for SOFT_SW GPIO keys

ARM: dts: koelsch: Configure pull-up for SOFT_SW GPIO keys

The GPIO pins connected to the 4 Software Switches ("SOFT_SW", SW2) do
not have external pull-up resistors, but rely on internal pull-ups being
enabled.  Fortunately this is satisfied by the initial state of these
pins.

Make this explicit by enabling bias-pull-up, to remove the dependency on
initial state and/or boot loader configuration.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Link: https://lore.kernel.org/r/20210303132941.3938516-1-geert+renesas@glider.be