kbuild: fix bzImage build for x86

As has been discussed previously (and Sam has been CC'ed), the fix
is still incorrect.  It replaces "echo -ne" with "/bin/echo -ne",
but neither of the two are guaranteed to support the necessary
arguments and necessary (hexadecimal) escape sequences.  What should
be used here is printf(1).  The trivial patch below (on top of these
kbuild changes) fixes this issue.

Signed-Off-By: Michael Tokarev <mjt@tls.msk.ru>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Michal Marek <mmarek@suse.cz>