Fix: Show string "Layout" if only single valid IME exists

From UX mocks, we need to show IME names in heading if there
are multiple IMEs. But in situation where we have multiple
IMEs but one of the IMEs doesn't have any valid subtype for PK,
it should work as if there is only a single IME.

Bug: 361528038
Test: manual
Flag: EXEMPT bugfix
Change-Id: Idd03a224b300df31b3265a5d58f79c0fc5d1535a