MAINTAINERS: update file list for MediaTek ARM platform

Add driver files for MediaTek ARM platform

diff --git a/MAINTAINERS b/MAINTAINERS
index 5a575f4..e0e9edd 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -412,9 +412,13 @@
 F:	drivers/phy/phy-mtk-*
 F:	drivers/pinctrl/mediatek/
 F:	drivers/power/domain/mtk-power-domain.c
+F:	drivers/pci/pcie_mediatek_gen3.c
+F:	drivers/pci/pcie_mediatek.c
+F:	drivers/pwm/pwm-mtk.c
 F:	drivers/ram/mediatek/
 F:	drivers/spi/mtk_snfi_spi.c
 F:	drivers/spi/mtk_spim.c
+F:	drivers/spi/mtk_snor.c
 F:	drivers/timer/mtk_timer.c
 F:	drivers/usb/host/xhci-mtk.c
 F:	drivers/usb/mtu3/
@@ -422,6 +426,7 @@
 F:	drivers/net/mtk_eth.c
 F:	drivers/net/mtk_eth.h
 F:	drivers/reset/reset-mediatek.c
+F:	drivers/serial/serial_mtk.c
 F:	include/dt-bindings/clock/mediatek,*
 F:	include/dt-bindings/power/mediatek,*
 F:	tools/mtk_image.c