mwifiex: print sleep_confirm cmd/response and power save events

Sleep Confirm command is sent separately while other commands
are handled through cmd_pending_q. Print sleep_confirm cmd and
its response as well as power save events so that we have a
clearer picture of power save handshake in driver log.

Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>