asm-generic: hook up new system calls

sys_rt_tgsigqueueinfo and sys_perf_counter_open
have been added in 2.6.31, so hook them up in the
generic unistd.h file.

Since the file is now in the mainline kernel, we
are no longer reordering the numbers but just add
system calls at the end.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>