Revert "cfg80211: remove enum ieee80211_band"

This reverts commit ee614382 ("cfg80211: remove enum ieee80211_band")
which is incomplete cherry-pick of commit 57fbcce37be7
("cfg80211: remove enum ieee80211_band") from
git://git.kernel.org/pub/scm/linux/kernel/git/jberg/mac80211-next.git


and due to which compilation of ath10k module is broken.

Incomplete cherry-pick means not all files of corresponding commit from
opensource repo are pulled.

Conflicts were resolved in drivers/net/wireless/ath/ath10k/htt_rx.c

CRs-Fixed: 1113043
Change-Id: Ie2f95b1524777e8eaf1436ba3e4ab3f9e6b2822e
Signed-off-by: Rajeev Kumar Sirasanagandla <rsirasan@codeaurora.org>