The current VEX code is not properly handling a non-zero TH field in the
dcbt instruction, which is valid for several forms of data cache block
touch instructions.  The VEX commit 2761 fixed the missing support in
VEX/priv/guest_ppc_toIR.c.  This commit adds tests for the the non-zero
fields to the test cases for 32 and 64-bit modes.

Bugzilla 324518

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@13534 a5019735-40e9-0310-863c-91ae7b9d1cf9