powerpc: add vcmpequd/vcmpequb ppc instruction macro

Some old tool chains don't know about instructions like vcmpequd.

This patch adds .long macro for vcmpequd and vcmpequb, which is
a preparation to optimize ppc64 memcmp with VMX instructions.

Signed-off-by: Simon Guo <wei.guo.simon@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>