pnv/xive2: TIMA support for 8-byte OS context push for PHYP

pnv/xive2: TIMA support for 8-byte OS context push for PHYP

PHYP uses 8-byte writes to the 2nd doubleword of the OS context
line when dispatching an OS level virtual processor.  This
support was not used by OPAL/Linux and so was never added.

Without this support, the XIVE code doesn't notice that a new
context is being pushed and fails to check for unpresented
pending interrupts for that context.

Signed-off-by: Glenn Miles <milesg@linux.vnet.ibm.com>
Signed-off-by: Michael Kowal <kowal@linux.ibm.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>