ia64: add an offset for system call number

The system call number in ia64 architecture starts with 1024.
But most of the other architecute starts with 0. In order to
come up with a common implementation to generate uapi header
we need to add an offset - __NR_Linux with a value 1024.

One of the patch in this patch series does have a script to
generate uapi header which uses syscall.tbl file. In syscall-
.tbl contain system call number. With the use of __NR_Linux,
we can start the number from 0 instead of 1024.
Signed-off-by: Firoz Khan <firoz.khan@linaro.org>
Signed-off-by: Tony Luck <tony.luck@intel.com>