wifi: ath12k: generalize GI and LTF fixed rate functions

wifi: ath12k: generalize GI and LTF fixed rate functions

Currently, functions in mac.c for setting GI and LTF rates are
specifically for HE rates.

Remove any mention of "HE" in such functions in order to allow for
other modes to utilize the functions. The intention is to prepare for
the addition of EHT GI and LTF fixed rate settings.

Tested-on: QCN9274 hw2.0 PCI WLAN.WBE.1.0.1-00029-QCAHKSWPL_SILICONZ-1

Signed-off-by: Muna Sinada <muna.sinada@oss.qualcomm.com>
Reviewed-by: Vasanthakumar Thiagarajan <vasanthakumar.thiagarajan@oss.qualcomm.com>
Link: https://patch.msgid.link/20251024001928.257356-2-muna.sinada@oss.qualcomm.com
Signed-off-by: Jeff Johnson <jeff.johnson@oss.qualcomm.com>