The behaviour of try_to_unmap_one() is difficult to follow because it
performs different operations based on a fairly large set of flags used
in different combinations.
TTU_MUNLOCK is one such flag. However it is exclusively used by
try_to_munlock() which specifies no other flags. Therefore rather than
overload try_to_unmap_one() with unrelated behaviour split this out into
it's own function and remove the flag.
Signed-off-by: Alistair Popple <apopple@xxxxxxxxxx>