wifi: wilc1000: remove suspend/resume from cfg80211 part

WILC1000 suspend/resume implementation is currently composed of two parts:
suspend/resume ops implemented in cfg80211 ops, which merely sets a
flag, and suspend/resume ops in sdio/spi driver which, based on this flag,
execute or not the suspend/resume mechanism. This dual set of ops is not
really needed , so keep only the sdio part to implement suspend/resume.

While doing so, remove the now unused suspend_event flag.

Signed-off-by: Alexis Lothoré <alexis.lothore@bootlin.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://msgid.link/20240613-wilc_suspend-v1-5-c2f766d0988c@bootlin.com