ppc4xx: Make Sequoia boot vxWorks

vxWorks expects in
TLB 0 a entry for the Machine Check interrupt
TLB 1 a entry for the RAM
TLB 2 a entry for the EBC
TLB 3 a entry for the boot flash

After changing the baudrate to 9600 I had no problems to boot the
vxWorks image as distributed by WindRiver (Revision 2.0/1 from
June 18, 2007)

Signed-off-by: Niklaus Giger <niklaus.giger@netstal.com>