UAPI: Fix arch/mips/include/asm/Kbuild to have separate header-y lines

Fix arch/mips/include/asm/Kbuild to have a separate header-y line for each
header to make them easier to relocate individually as part of the UAPI header
split.

Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Ralf Baechle <ralf@linux-mips.org>