8852C add new hardware feature -- preload window, which is used to load
more data to D-MAC, so it can possibly yield better performance.

This patch is to configure preload and reserved size for next window.
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20220317055543.40514-8-pkshih@realtek.com