gpu: drm: udl: Adding new typedef vm_fault_t

Use new return type vm_fault_t for fault and huge_fault
handler. For now, this is just documenting that the
function returns a VM_FAULT value rather than an errno.
Once all instances are converted, vm_fault_t will become
a distinct type.

Commit 1c8f4220 ("mm: change return type to vm_fault_t")

Previously vm_insert_page() returns err which driver
mapped into VM_FAULT_* type. The new function vmf_
insert_page() will replace this inefficiency by
returning VM_FAULT_* type.

Signed-off-by: Souptick Joarder <jrdr.linux@gmail.com>
Reviewed-by: Matthew Wilcox <mawilcox@microsoft.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20180425045922.GA21590@jordon-HP-15-Notebook-PC