x86/platform/uv: Fix calculation of Global Physical Address

The calculation of the global physical address (GPA) on UV4 is
incorrect.  The gnode_extra/upper global offset should only be
applied for fixed address space systems (UV1..3).

Tested-by: John Estabrook <john.estabrook@hpe.com>
Signed-off-by: Mike Travis <mike.travis@hpe.com>
Cc: Dimitri Sivanich <dimitri.sivanich@hpe.com>
Cc: John Estabrook <estabrook@sgi.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Russ Anderson <russ.anderson@hpe.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170321231646.667689538@asylum.americas.sgi.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>