The last two 8MB TLB entries are being incorrectly set by initial_mmu on 8xx.

The first entry is written with the same virtual/physical address, which
renders it invalid:

BDI>rms 792 0x00001e00
BDI>rms 824 1
BDI>rds 824
SPR  824 : 0xc08000c0  -1065353024
BDI>rds 825
SPR  825 : 0xc0800de0  -1065349664
BDI>rds 826
SPR  826 : 0x00000000            0

And the second entry, in addition, does not have its TLB index set
correctly.
Signed-off-by: Marcelo Tosatti <marcelo.tosatti@cyclades.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>