HVM firmware passthrough SMBIOS processing

HVM firmware passthrough SMBIOS processing

Passthrough support for the SMBIOS structures including three new DMTF
defined types and support for OEM defined tables. Passed in SMBIOS
types override the default internal values. Default values can be
enabled for the new type 22 portable battery using a xenstore
flag. All other new DMTF defined and OEM structures will only be added
to the SMBIOS table if passthrough values are present.

Signed-off-by: Ross Philipson <ross.philipson@citrix.com>
Committed-by: Keir Fraser <keir@xen.org>