MAINTAINERS: exclude maintained subdirs in RISC-V misc DT entry

The Allwinner & Renesas stuff doesn't go through my tree, so it is a wee
bit misleading to have them match against the "misc" entry in
MAINTAINERS.
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>

MAINTAINERS

@@ -18154,6 +18154,8 @@ Q:	https://patchwork.kernel.org/project/linux-riscv/list/
 T:	git https://git.kernel.org/pub/scm/linux/kernel/git/conor/linux.git/
 F:	Documentation/devicetree/bindings/riscv/
 F:	arch/riscv/boot/dts/
+X:	arch/riscv/boot/dts/allwinner/
+X:	arch/riscv/boot/dts/renesas/
 
 RNBD BLOCK DRIVERS
 M:	Md. Haris Iqbal <haris.iqbal@ionos.com>