target-ppc: Implement IVOR[59] By Default for Book E

Adjust the IVOR mask for generic Book E implementation to support bit 59.
This is consistent with the Power ISA.

Signed-off-by: Tom Musta <tommusta@gmail.com>
Reported-by: Pierre Mallard <mallard.pierre@gmail.com>
Signed-off-by: Alexander Graf <agraf@suse.de>