rtw89: extend mac tx_en bits from 16 to 32

In order to support 8852C that uses 32 bits to control TX types.

This patch doesn't really use 32 bits tx_en yet, but next patch will
use it.

Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20220317055543.40514-12-pkshih@realtek.com