This patch adds CPU dependent boot mode flag support.

Different CPUs use different bits for the boot mode flag.  The constant
MMU_BM is replaced with a variable which is set for the selected CPU.

This patch also removes the MMU flags from being saved in the
translation block code as a result of an off line discussion with Paul 
Brook.

This patch also performs a CPU reset after the CPU is registered rather
than before.

This patch has successfully booted the debian installer and the initrd 
kernel
in sparc-test successfully for both an ss5 and ss10.  It also makes running
an ss10 openboot rom image behave a little better.