qcacmn: Get BT/WLAN isolation for mainline

Propagation from qcacld2.0 to qcacld3.0.
The WMI CMD and EVENT of "get antenna isolation" are already defined,
but not used before in qcacld3.0.
Now, The host driver uses vendor command to get this information
instead of iwpriv command in qcacld-2.0.
The attribution of this feature is already defined in file
"qca_vendor.h". The name is "QCA_WLAN_VENDOR_ATTR_ANTENNA_ISOLATION".
So host driver will use vendor command
"QCA_NL80211_VENDOR_SUBCMD_GET_HW_CAPABILITY" to get the information
from lower layer.
Change-Id: I915768f622ddc9a70a95ce4fe952f19917a8f901
CRs-Fixed: 2447363