Check to see if `${CROSS_COMPILE}mkimage` exists and if not, fall back to
the standard `mkimage`

The Blackfin toolchain includes mkimage, but we dont want to namespace
collide with any of the user's system setup, so we prefix it with our
toolchain name.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Oleg Verych <olecom@flower.upol.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.

Let it rip!