firmware, DMI: Add function to look up a handle and return DIMM size

When we first scan the SMBIOS table, save the size of the DIMM.

Provide a function for other code (EDAC driver) to look up the size
of a DIMM from its SMBIOS handle.

Reviewed-by: Jean Delvare <jdelvare@suse.de>
Signed-off-by: Tony Luck <tony.luck@intel.com>
Cc: Aristeu Rozanski <aris@redhat.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Len Brown <lenb@kernel.org>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Cc: Qiuxu Zhuo <qiuxu.zhuo@intel.com>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: linux-acpi@vger.kernel.org
Cc: linux-nvdimm@lists.01.org
Link: http://lkml.kernel.org/r/20180312182430.10335-5-tony.luck@intel.com
Signed-off-by: Borislav Petkov <bp@suse.de>