ppc/xive2: Update NVP save/restore for group attributes

ppc/xive2: Update NVP save/restore for group attributes

If the 'H' attribute is set on the NVP structure, the hardware
automatically saves and restores some attributes from the TIMA in the
NVP structure.

The group-specific attributes LSMFB, LGS and T have an extra flag to
individually control what is saved/restored.

Signed-off-by: Frederic Barrat <fbarrat@linux.ibm.com>
Signed-off-by: Michael Kowal <kowal@linux.ibm.com>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>