checkpatch: types: some types may also be identifiers

Some types such as typedefs may overlap real identifiers.  Be more
targetted about when a type can really exist.  Where it cannot let it be
an identifier.  This prevents false reporting of the minus '-' in unary
context in the following:

	foo[bar->bool - 1];

Signed-off-by: Andy Whitcroft <apw@shadowen.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>