dt-bindings: input: touchscreen: imagis: add missing minItems

dt-bindings: input: touchscreen: imagis: add missing minItems

The binding currently expects exactly 5 keycodes, which matches the
chip's theoretical maximum but probably not the number of touch keys on
any phone using the IST3032C. Add a minItems value of 2 to prevent
dt-validate complaints.

Also add another example to make sure the linux,keycodes property is
checked.

Signed-off-by: Duje Mihanović <duje@dujemihanovic.xyz>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20250824-imagis-minitems-v1-1-cea9db55e87f@dujemihanovic.xyz
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>