qtnfmac: convert channel width from bitfiled to simple enum

This will allow to use qlink channel width values to specify BW setting
corresponding to enum nl80211_chan_width.
Current user is converted to apply BIT() macro manually to each individual
qlink_channel_width enumeration value.

Signed-off-by: Igor Mitsyanko <igor.mitsyanko.os@quantenna.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>