counter: interrupt-cnt: Implement watch_validate callback

counter: interrupt-cnt: Implement watch_validate callback

The interrupt-cnt counter driver only pushes one type of event on only
one channel: COUNTER_EVENT_CHANGE_OF_STATE on channel 0. The
interrupt_cnt_watch_validate() watch_valid callback is implemented to
ensure watch configurations are valid for this driver.

Cc: Oleksij Rempel <linux@rempel-privat.de>
Cc: Pengutronix Kernel Team <kernel@pengutronix.de>
Link: https://lore.kernel.org/r/20220815225058.144203-1-william.gray@linaro.org/
Signed-off-by: William Breathitt Gray <william.gray@linaro.org>
Link: https://lore.kernel.org/r/c50b5eede7d3f523de8dc3937dc44680f2773e1d.1664318353.git.william.gray@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>