ARM: 8893/1: boot: Explain the 8 nops

This was unclear to me until Russell explained the obvious
that 8 nops are added to offset an a.out image. Reading
git history reveals that thumb kernels first removed the
nops and then kept 7 of them (the last instruction being
a switch to thumb mode) as it turns out that some boot
loaders were using this as a "patch area". Also the magic
numbers after the initial nops and the jump of course
need to stay in the same offset for kernel file
detection.

Make the code easier to understand with a comment.

Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Nicolas Pitre <nico@fluxnic.net>
Acked-by: Roy Franz <rfranz@marvell.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>