ARM: dts: rskrza1: Add input switches

Add support for input switches SW1-3 on the Renesas RZ/A1 RSK+RZA1
development board.

Note that this uses the IRQ interrupts, as the RZ/A1 GPIO controller
does not include interrupt support.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>