Initial ISA 2.07 support for POWER8-tuned libc

The IBM Power ISA 2.07 has been published on power.org, and IBM's new POWER8
processor is under development to implement that ISA. This patch provides
initial VEX support for running Valgrind on POWER8 systems running a soon-to-be
released Linux distribution. This Linux distro will include a POWER8-tuned
libc that uses a subset of the new instructions from ISA 2.07. Since virtually
all applications link with libc, it would be impossible to run an application
under Valgrind on this distro without adding support for these new instructions
to Valgrind, so that's the intent of this patch. Note that applications built
on this distro will *not* employ new POWER8 instructions by default. There are
roughly 150 new instructions in the Power ISA 2.07, including hardware
transaction management (HTM). Support for these new instructions (modulo the
subset included in this bug) will be added to Valgrind in a phased approach,
similar to what we did for Power ISA 2.06.

Bugzilla 322294

git-svn-id: svn://svn.valgrind.org/vex/trunk@2740 8f6e269a-dfd6-0310-a8e1-e2731360e62c