Fix kernel module

 - Fix path in Kbuild and slkm_init.c
 - Specify in README that configure must be called with --disable-wchar
to build kernel module (as wchar is not available in kernel space)
 - Include config.h in kernel mode (for restrict define if needed)
 - Fix calls to EXPORT_SYMBOL in all files (missing trailing ;)
 - Do not include time.h in kernel space
 - Do not declare functions that use FILE in kernel space
 - Do not define handle_werror in safe_str_constraint.h if wchar is
disabled

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>