wifi: ath12k: refactor SMPS configuration

Move fetching SMPS value to a new function and use u16_get_bits
to extract it from capabilities. This will help in extending the
functionality when SMPS support in 6 GHz band gets added in
subsequent patches.

Tested-on: QCN9274 hw2.0 PCI WLAN.WBE.1.0.1-00029-QCAHKSWPL_SILICONZ-1
Tested-on: WCN7850 hw2.0 PCI WLAN.HMT.1.0.c5-00481-QCAHMTSWPL_V1.0_V2.0_SILICONZ-3

Signed-off-by: Pradeep Kumar Chitrapu <quic_pradeepc@quicinc.com>
Acked-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://msgid.link/20240508173655.22191-6-quic_pradeepc@quicinc.com