arm64: dmi: set DMI string as dump stack arch description

This sets the DMI string, containing system type, serial number,
firmware version etc. as dump stack arch description, so that oopses
and other kernel stack dumps automatically have this information
included, if available.

Tested-by: Leif Lindholm <leif.lindholm@linaro.org>
Acked-by: Leif Lindholm <leif.lindholm@linaro.org>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>