arm64: dts: k3-j721e: Add gpio-keys on common processor board

Common processor board for K3 J721E platform has two push buttons
namely SW10 and SW11.
Add a gpio-keys device node to model them as input keys in Linux.
Add required pinmux nodes to set GPIO pins as input.

Signed-off-by: Nikhil Devshatwar <nikhil.nd@ti.com>
Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
Reviewed-by: Keerthy <j-keerthy@ti.com>
Signed-off-by: Tero Kristo <t-kristo@ti.com>