x86, uv: use consistent names for region size and conherence id on x86 and ia64

Use consistent names for region size and conherence id on x86 and ia64.

The SGI xp drivers are used on both ia64 and x86.  Using the same
names (sn_coherency_id, sn_region_size) simplies the driver code.

Signed-off-by: Russ Anderson <rja@sgi.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>