target-ppc: Load Quadword

This patch adds the Book I (user space) Load Quadword (lq) instruction.
This instruction was introduced into Book I in Power ISA V2.07.  Previous
versions of the architecture supported this as a privileged instruction.
Previous versions of the architecture also did not support Little Endian
mode.

Note that this patch also adds the PPC_64BX flag to the Power8 model,
which enables the lq instruction.

Signed-off-by: Tom Musta <tommusta@gmail.com>
Signed-off-by: Alexander Graf <agraf@suse.de>
