Sparc64 has a way of providing the base address for the per cpu area of the
currently executing processor in a global register.

Sparc64 also provides a way to calculate the address of a per cpu area
from a base address instead of performing an array lookup.

Cc: David Miller <davem@davemloft.net>
Signed-off-by: Mike Travis <travis@sgi.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>