SGI IA64 UV: fix ia64 build error in the linux-next tree

Fix the ia64 build error that occurs in the linux-next tree by introducing
an ia64 version of uv.h.

Additionally, clean up the usage of is_uv_system().

Signed-off-by: Dean Nelson <dcn@sgi.com>
Signed-off-by: Jack Steiner <steiner@sgi.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>