wifi: ath12k: use fw_features only when it is valid

wifi: ath12k: use fw_features only when it is valid

Currently fw_features is used to check if a specific feature is supported
or not: if the feature bit is set the feature is believed to be supported,
otherwise not supported. Since fw_features is populated only when using
firmware API-2, and by default it is zero, in case of API-1 such as
WCN7850 firmware it is possible that a feature is not enabled by host
while actually firmware supports it.

To avoid this, add a new flag indicating whether fw_features has been ever
populated or not, and only when that flag is true we choose to believe
fw_features. This benefits firmware MLO capability validation in an
upcoming patch.

Tested-on: WCN7850 hw2.0 PCI WLAN.HMT.1.0.c5-00481-QCAHMTSWPL_V1.0_V2.0_SILICONZ-3
Tested-on: WCN7850 hw2.0 PCI WLAN.HMT.1.1.c5-00284-QCAHMTSWPL_V1.0_V2.0_SILICONZ-1
Tested-on: QCN9274 hw2.0 PCI WLAN.WBE.1.3.1-00209-QCAHKSWPL_SILICONZ-1

Signed-off-by: Baochen Qiang <quic_bqiang@quicinc.com>
Link: https://patch.msgid.link/20250409-ath12k-wcn7850-mlo-support-v2-2-3801132ca2c3@quicinc.com
Signed-off-by: Jeff Johnson <jeff.johnson@oss.qualcomm.com>