When elements are 64 bits, the vec_st_interleave()/vec_ld_deinterleave()
doesn't interleave 4 elements correctly.

For vec_st_interleave(), following is saved into mem:
	a0 b0 a1 b1 c0 d0 c1 d1
     -> we expected:
	a0 b0 c0 d0 a1 b1 c1 d1

for vec_ld_deinterleave(), following is loaded into a b c d for memory
string { 1 2 3 4 5 6 7 8 }:
	a: 1 3
	b: 2 4
	c: 5 7
	d: 6 8
   -> we expected:
   	a: 1 5
	b: 2 6
	c: 3 7
	d: 4 8

This patch corrects this behavior.
Signed-off-by: Simon Guo <wei.guo.simon@gmail.com>