Input: samsung-keypad - clean up wakeup configuration logic

When checking if the device can wake the system, we should pull the
device_may_wakeup() check to the caller instead of repeating it inside
the toggle_wakeup() handler. Furthermore, when configuring the wakeup,
we should safely ensure we write to the registers in the correct order:
configure the interrupt receiver before enabling the peripheral's wake
functionality, and vice-versa.

Assisted-by: Antigravity:gemini-3.1-pro
Link: https://patch.msgid.link/20260713-samsung-kp-irq-v2-1-acc84b6daf9a@gmail.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>