Further fixes on top of 9e2f316ed. Writing some doco for gcc on
inline assembly woke me up to some more errors.
- dgemv_kernel_4x4 asm did not mention *ap as a memory input, and
*y is both read and write.
- sasum_kernel_32 and casum_kernel_16 did not use %x for a vsx insn
operand, a problem if the "=f" sum output was ever allocated a vsx
reg in the altivec set. This might be possible with inlining and
future gcc optimisation.
dc40bc7368