[PARISC] Reorder syscalls to match unistd.h

Move migrate_pages into the same position as specified
in unistd.h. This fixes migrate_pages, pselect6 and
ppoll syscalls.

Signed-off-by: Carlos O'Donell <carlos@systemhalted.org>
Signed-off-by: Kyle McMartin <kyle@parisc-linux.org>