selinux: Add export.h to files using EXPORT_SYMBOL/THIS_MODULE

The pervasive, but implicit presence of <linux/module.h> meant
that things like this file would happily compile as-is.  But
with the desire to phase out the module.h being included everywhere,
point this file at export.h which will give it THIS_MODULE and
the EXPORT_SYMBOL variants.

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>