s390/mm,fault: simplify kfence fault handling

do_no_context() can be simplified by removing its fault parameter,
which is only used to decide if kfence_handle_page_fault() should be
called.

If the fault happened within the kernel space it is ok to always check
if this happened on a page which was unmapped because of the kfence
feature. Limiting the check to the VM_FAULT_BADCONTEXT case doesn't
add any value.

Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>