x86, 64-bit: print DMI info in the oops trace

This patch echoes what we already do on 32-bit since
90f7d25c

, and prints the DMI
product name in show_regs, so that system specific problems can be
easily identified.

Signed-off-by: Kyle McMartin <kyle@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>