arm64: dts: mediatek: don't include missing file

This resolves a build error in the next/dt branch:

In file included from arch/arm64/boot/dts/mediatek/mt6797-evb.dts:16:0:
arch/arm64/boot/dts/mediatek/mt6797.dtsi:15:10: fatal error: dt-bindings/power/mt6797-power.h: No such file or directory

003f5d0c

 ("arm64: dts: mediatek: add clk and scp nodes for MT6797")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>