Kbuild: Fix cleanup of *.dtb for some archs

'make clean' did not descend into arch/$ARCH/dts for arc, m68k, nios2,
sh, xtensa.

Fix it by adding the missing archs to the explicit clean-dirs list.

Signed-off-by: Tobias Deiminger <tdmg@linutronix.de>
1 file changed