sparc32: drop fixmap.h

sparc32 does not support fixmaps - so do not pretend so by
having the fixmap.h file.
Move relevant parts to vaddrs.h.

I looked at simplifying this even more but failed to understand
the reasoning behind the extra guard page involved and due to
missing testing possibilities only the trivial conversion was done.

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