ath11k: Move mac80211 hw allocation before wmi_init command

This is to prepare REO ring setup before sending wmi_init command.
Firmware expects all the required REO rings to be setup while processing
wmi_init command. But as per the current initialization sequence, REO ring
configurations are done only after wmi_init command is sent.
Also refactoring ath11k_mac_create() into ath11k_mac_alloc() and
ath11k_mac_register() to it mac80211 hw structure available before sending
wmi_init command.

Signed-off-by: Vasanthakumar Thiagarajan <vthiagar@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>