powerpc: Add driver for Barrier Synchronization Register

Adds a character driver for BSR support on IBM POWER systems including
Power5 and Power6.  The BSR is an optional processor facility not currently
implemented by any other processors.  It's primary purpose is fast large SMP
synchronization.  More details on the BSR are in comments to the code which
follows.  This patch adds BSR driver to pseries_defconfig.

Signed-off-by: Sonny Rao <sonnyrao@linux.vnet.ibm.com>
Signed-off-by: Joel Schopp <jschopp@austin.ibm.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>