sparc32: drop prom version check in head_32.S

We already sorted out if we are a sun4/sun4c and halted.
So no need to check the prom version as we know this is
a v2 or v3 as sun4m, sun4d etc. does not use a v1 prom.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: David S. Miller <davem@davemloft.net>