PPC64, fix issues with dnormal values in the vector fp instructions.

PPC64, fix issues with dnormal values in the vector fp instructions.

The result of the floating point instructions vmaddfp, vnmsubfp,
vaddfp, vsubfp, vmaxfp, vminfp, vrefp, vrsqrtefp, vcmpeqfp, vcmpeqfp,
vcmpgefp, vcmpgtfp are controlled by the setting of the NJ bit in
the VSCR register.  If VSCR[NJ] = 0; then denormalized values are
handled as specified by Java and the IEEE standard.  If the bit is
a 1, then the denormalized element in the vector is replaced with
a zero.

Valgrind was not properly handling the denormalized case for these
instructions.  This patch fixes the issue.

https://bugs.kde.org/show_bug.cgi?id=406256