wifi: rtw88: refine register based H2C command

Since register based H2C commands don't need endian conversion.
Introduce a new API that don't do conversion and send it directly.
New caller are expected to encode with cpu order and gradually
replace the old ones.

Signed-off-by: Po-Hao Huang <phhuang@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20230616125540.36877-6-pkshih@realtek.com