devicetree: use wildcard to clean arch subdir

Use wildcard to clean arch subdirectories, as it is cleaner than
listing all the arch which builds dtb.

Signed-off-by: Thomas Chou <thomas@wytron.com.tw>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>

dts/Makefile

@@ -45,4 +45,4 @@ dtbs: $(obj)/dt.dtb
 clean-files := dt.dtb.S
 
 # Let clean descend into dts directories
-subdir- += ../arch/arm/dts ../arch/microblaze/dts ../arch/mips/dts ../arch/sandbox/dts ../arch/x86/dts
+subdir- += ../arch/*/dts