ARM: 7152/1: distclean: Remove generated .dtb files

http://git.omapzoom.org/?p=kernel/omap.git;a=blobdiff;f=arch/arm/boot/Makefile;h=5df26a9976a26c10ddfcf0f788302dd2caeb8769;hp=176062ac7f07305014357372c42285ff07a09c68;hb=5f300acd8ae9f3d4585154370012ffc5c665330f;hpb=8428e84d42179c2a00f5f6450866e70d802d1d05