Update cffi_support.py

This pull request fixes a few issues:
* Add missing `numba.` prefix before `struct`
* Add a few more basic types supported by cffi
* `type.fields` returns fields, not types
* Basic types (like `uint32_t`) don't seem to have `kind`

I tested this with cffi 0.7.2, numba 0.10 and the following code.

```python
from cffi import FFI
from numba.support.cffi_support import map_type

ffi = FFI()
ffi.cdef('''
typedef struct INPUT_ {
	uint32_t test;
} INPUT;
''')

print map_type(ffi.typeof('INPUT'));
```