wil6210: force EDMG channel through debugfs

Force EDMG (Enhanced Directional Multi-Gigabit) channel through debugfs
for debugging channel bonding feature.

Usage: echo <EDMG_CH> > force_edmg_channel

When force_edmg_channel is set, it will be used in connect and PCP start
commands.

Change-Id: Ia1e12cb8cf730dbb448fae47b40dfa11053567d0
Signed-off-by: Alexei Avshalom Lazar <ailizaro@codeaurora.org>
Signed-off-by: Maya Erez <merez@codeaurora.org>