MAINTAINERS: wifi: add git tree for Realtek WiFi drivers

Add git tree to manage all Realtek WiFi drivers except RTL8180 which is
old and orphan.

Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://msgid.link/20240319011925.6855-1-pkshih@realtek.com