brcm80211: smac: removed down-on-watchdog MPC functionality

Softmac would bring its interface down on a certain Minimum Power Save
related condition, without Mac80211 intervention. Because Mac80211 should
be the only party initiating interfaces going up and down, this functionality
has been removed. All notions of 'MPC' have been removed in the code as
well.

Reviewed-by: Alwin Beukers <alwin@broadcom.com>
Reviewed-by: Arend van Spriel <arend@broadcom.com>
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Signed-off-by: Roland Vossen <rvossen@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>