rtw89: add chip_info::h2c_desc_size/fill_txdesc_fwcmd to support new chips

8852A and 8852C use different H2C header and size, so add h2c_desc_size
to allocate different header size and fill content by fill_txdesc_fwcmd.

Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20220318023214.32411-8-pkshih@realtek.com