powerpc/xmon: Add dl command to dump contents of __log_buf

Hello All,

Quite a while back Michael Ellerman had posted a patch to add support to xmon to print the contents of the console log pointed to by __log_buf.
Here's the link to that patch - http://ozlabs.org/pipermail/linuxppc64-dev/2005-March/003657.html
I've ported the patch in the above link to 2.6.30-rc5 and have tested it.

Thanks & regards,
Vinay

Signed-off-by: Michael Ellerman <michael at ellerman.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>