[XEN][POWERPC] Print DAR and DSISR registers on CPU register dumps

[XEN][POWERPC] Print DAR and DSISR registers on CPU register dumps

The information from these register can really help track doen
problems.  They are only saved on program exception, so we show what
in the CPU at time of printing as well.

Signed-off-by: Jimi Xenidis <jimix@watson.ibm.com>
--HG--
extra : transplant_source : %B4%B7%24%9F%00%D6%062%86%D8%D7%24%0FCA%E0%8B%D2%EE%91