ARM: dts: koelsch: Rename sw2 to keyboard

Rename "sw2_pins" and "sw2" to "keyboard_pins" resp. "keyboard", to
comply with generic name recommendations.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Link: https://lore.kernel.org/r/3d718cf69e21b1ceea0c29c0e841b9bdda44533d.1619785905.git.geert+renesas@glider.be