DESC
Adds the arch-independent part of SKAS3 support.
EDESC
Adds the arch-independent part of SKAS3 support.

Fixes merged here:

* Make SKAS and UML compile-time compatible
Avoid UML (and other archs, too) failing compilation when the SKAS+SYSEMU
patch is applied.

* Avoid using current->mm while processing a /proc/mm request.
1) We have first a little fix for mprotect, which made it not work at all
and completely (which could explain why Java crashes Uml).
Actually, mprotect() worked onto the UML kernel address space.

2) part of do_mmap_pgoff (actually arch_get_unmapped_area) has the same
bug, except if we call it with MAP_FIXED (as UML always does, see
arch/um/kernel/skas/mem_user.c:map()). So return -EINVAL otherwise
(actually, if we want to implement that later, we could return ENOSYS or
ENODEV, but for now the idea is that the interface only allows MAP_FIXED
mappings). Obviously, for SKAS4 it's a different matter, but in SKAS4
it will work obviously.