[ARM] nommu: trivial fixups for head-nommu.S and the Makefile

This patch fix compilation problem of start-up codes.
(head-nommu.S, arch/arm/kernel/Makefile)

Signed-off-by: Hyok S. Choi <hyok.choi@samsung.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>