[ARM] nommu: add nommu specific Kconfig and MMUEXT variable in Makefile

This patch adds Kconfig-nommu for noMMU specific configurations
and MMUEXT variable into Makefile.

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