MAINTAINERS: MediaTek: add USB related files

Add dt-binding files of xhci-mtk and phys, C files of
phys.

Signed-off-by: Frank Wunderlich <frank-w@public-files.de>
diff --git a/MAINTAINERS b/MAINTAINERS
index 66f0b07..ec59ce8 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -244,9 +244,12 @@
 F:	arch/arm/mach-mediatek/
 F:	arch/arm/include/asm/arch-mediatek/
 F:	board/mediatek/
+F:	doc/device-tree-bindings/phy/phy-mtk-*
+F:	doc/device-tree-bindings/usb/mediatek,*
 F:	doc/README.mediatek
 F:	drivers/clk/mediatek/
 F:	drivers/mmc/mtk-sd.c
+F:	drivers/phy/phy-mtk-*
 F:	drivers/pinctrl/mediatek/
 F:	drivers/power/domain/mtk-power-domain.c
 F:	drivers/ram/mediatek/