kexec: Fix make headers_check

kexec: Fix make headers_check

Remove the unneded declaration for a kexec_load() routine.

Fixes errors like these when running 'make headers_check':

include/uapi/linux/kexec.h: userspace cannot reference function or variable defined in the kernel

Paul said:

: The kexec_load declaration isn't very useful for userspace, see the patch
: I submitted in http://lkml.kernel.org/r/1389791824.17407.9.camel@x220 .
: And After my attempt the export of that declaration has also been
: discussed in
: http://lkml.kernel.org/r/115373b6ac68ee7a305975896e1c4971e8e51d4c.1408731991.git.geoff@infradead.org
:
: In that last discussion no one has been able to point to an actual user of
: it.  So, as far as I can tell, no one actually uses it.  Which makes
: sense, because including this header by itself doesn't give one access to
: a useful definition of kexec_load.  So why bother with the declaration?

Signed-off-by: Geoff Levand <geoff@infradead.org>
Acked-by: Paul Bolle <pebolle@tiscali.nl>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Maximilian Attems <max@stro.at>
Cc: Michal Marek <mmarek@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
[sw0312.kim: cherry-pick mainline commit 9dc5c05f45ca for gcc 9 build]
Signed-off-by: Seung-Woo Kim <sw0312.kim@samsung.com>
Change-Id: I6fa5f13b9799c7a648fe93aa40648bfaf8f380e9