xtensa: types: use <asm-generic/int-*.h> for the xtensa architecture

This modifies <asm-xtensa/types.h> to use the <asm-generic/int-*.h>
generic include files.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Cc: Chris Zankel <chris@zankel.net>