[SPARC64]: Remove unnecessary paging_init() cruft.

Because we don't access the PAGE_OFFSET linear mappings
any longer before we take over the trap table from the
firmware, we don't need to load dummy mappings there
into the TLB and we don't need the bootmap_base hack
any longer either.

While we are here, check for a larger than 8MB kernel
and halt the boot with an error message.  We know that
doesn't work, so instead of failing mysteriously we
should let the user know exactly what's wrong.

Signed-off-by: David S. Miller <davem@davemloft.net>