net: dsa: bcm_sf2: Make SF2_IO64_MACRO() utilize 32-bit macro

There is no point inlining the 32-bit direct register read/write part,
just infer it from the existing macro. This will make it easier to
centralize the address rewriting that we are going to introduce later
on.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>