powerpc/pseries: Inform the hypervisor we are using EBB regs

On LPAR systems we need to inform the hypervisor that we are using the
EBB registers. We do this by setting a bit in the Virtual Processor Area
(VPA) - formerly known as the lppaca.

For now we do this always, ie. we do not dynamically enable/disable.

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>