[PATCH] ppc64: Add PTRACE_{GET|SET}VRREGS

The ptrace get and set methods for VMX/Altivec registers present in the
ppc tree were missing for ppc64.  This patch adds the 32-bit and
64-bit methods.  Updated with the suggestions from Anton following the lines
of his code snippet.

Added:
 - flush_altivec_to_thread calls as suggested by Anton
 - piecewise copy of structure to preserve 32-bit vrsave data as per
   Anton

(I consolidated the 32 and 64bit versions with 2 helper macros - Anton)

Signed-off-by: Robert C Jennings <rcjenn@austin.ibm.com>
Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>