ath11k: add support for setting fixed HE rate/gi/ltf

Support setting fixed HE rate/gi/ltf values that we are now able to send
to the kernel using nl80211. The added code is reusing parts of the
existing code path already used for HT/VHT. The new helpers are
symmetric to how we do it for HT/VHT.

Tested-on: IPQ8074 hw2.0 AHB WLAN.HK.2.5.0.1-00235-QCAHKSWPL_SILICONZ-1

Signed-off-by: Miles Hu <milehu@codeaurora.org>
Co-developed-by: Aloka Dixit <alokad@codeaurora.org>
Signed-off-by: Aloka Dixit <alokad@codeaurora.org>
Co-developed-by: Lavanya Suresh <lavaks@codeaurora.org>
Signed-off-by: Lavanya Suresh <lavaks@codeaurora.org>
Co-developed-by: Pradeep Chitrapu <pradeepc@codeaurora.org>
Signed-off-by: Pradeep Chitrapu <pradeepc@codeaurora.org>
Signed-off-by: Venkateswara Naralasetty <vnaralas@codeaurora.org>
Signed-off-by: Jouni Malinen <jouni@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20210721173615.75637-1-jouni@codeaurora.org