fix asm-x86/{posix_types,unistd}.h

Jeff Chua reported that:

Commit e40c0fe6


(x86: cleanup duplicate includes) turned the userspace
asm-x86/posix_types.h and asm-x86/unistd.h headers into
empty files.

This patch reverts these bogus changes.

Reported-by: Jeff Chua <jeff.chua.linux@gmail.com>
Signed-off-by: Adrian Bunk <bunk@kernel.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>