Move module_enable_x() together with module_enable_nx() and
module_enable_ro().

Those three functions are going together, they are all used
to set up the correct page flags on the different sections.

As module_enable_x() is used independently of
CONFIG_STRICT_MODULE_RWX, build strict_rwx.c all the time and
use IS_ENABLED(CONFIG_STRICT_MODULE_RWX) when relevant.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>