Add support for the TEXASRU register. This register contains information on

Add support for the TEXASRU register.  This register contains information on
transactional memory instruction summary information.  This register contains
the upper 32-bits of the transaction information.  Note, the valgrind
implementation of transactional memory instructions is limited.  Currently, the
contents of the TEXASRU register will always return 0.  The lower 64-bits of
the trasnaction information in the TEXASR register will contain the failure
information as setup by Valgrind.

This commit contains the changes needed to support the TEXASRU register on
PPC64.

This support requires changing the value of MAX_REG_WRITE_SIZE in
memcheck/mc_main.c from 1696 to 1712.  The change is made in the corresponding
valgrind commit.

This patch addresses Bugzilla 346474

git-svn-id: svn://svn.valgrind.org/vex/trunk@3143