rfkill: add master_switch_mode and EPO lock to rfkill and rfkill-input

Add of software-based sanity to rfkill and rfkill-input so that it can
reproduce what hardware-based EPO switches do, blocking all transmitters
and locking down any further attempts to unblock them until the switch is
deactivated.

rfkill-input is responsible for issuing the EPO control requests, like
before.

While an rfkill EPO is active, all transmitters are locked to one of the
BLOCKED states and all attempts to change that through the rfkill API
(userspace and kernel) will be either ignored or return -EPERM errors.

The lock will be released upon receipt of EV_SW SW_RFKILL_ALL ON by
rfkill-input, or should modular rfkill-input be unloaded.

This makes rfkill and rfkill-input extend the operation of an existing
wireless master kill switch to all wireless devices in the system, even
those that are not under hardware or firmware control.

Since the above is the expected operational behavior for the master rfkill
switch, the EPO lock ...