fix xtensa timerfd breakage

In file included from /home/bunk/linux/kernel-2.6/git/linux-2.6/arch/xtensa/kernel/syscall.c:39:
include2/asm/unistd.h:681: error: 'sys_timerfd' undeclared here (not in a function)

Signed-off-by: Adrian Bunk <bunk@kernel.org>
Cc: Christian Zankel <chris@zankel.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>