iwlwifi: mvm: change when the BT_COEX is sent

The BT_COEX command should not be sent to the INIT
firmware image starting from 8000 family.
The firmware team also requested to send the BT_COEX
command after the PHY_DB_CMD and the PHY_CFG_CMD.

While at it:
s/iwl_send_bt_init_conf/iwl_mvm_send_bt_init_conf/

Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>