target-ppc: Disentangle get_physical_address() paths

Depending on the MSR state, for 64-bit hash MMUs, get_physical_address
can either call check_physical (which has further tests for mmu type)
or get_segment64.  Similarly for 32-bit hash MMUs we can either call
check_physucal or get_bat() and get_segment32().

This patch splits off the whole get_physical_addresss() path for hash
MMUs into 32-bit and 64-bit versions, handling real mode correctly for
such MMUs without going to check_physical and rechecking the mmu type.
Correspondingly, the hash MMU specific paths in check_physical() are
removed.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Alexander Graf <agraf@suse.de>
