wlan: Store avoid channel list

Store avoid channel list into recoverable location.
If Softap mode detects current channel is not safe to use,
WLAN kernel module will be restarted.
Then WLAN kernel module internal storage will lost
unsafe channel information.
To avoid start softap with unsafe channel, channel information
should be stored in static location.

Change-Id: I5a6d7ab7314936d7bbaaf7a005e58179a4dc0613
CRs-fixed: 576020
Signed-off-by: Leo Chang <leochang@codeaurora.org>