[smsc95xx] Fetch MAC from SMBIOS OEM string for Honeywell VM3

The Honeywell VM3 has no attached EEPROM, and records the MAC address
within an SMBIOS OEM string.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/include/ipxe/smbios.h

@@ -152,6 +152,9 @@ struct smbios_enclosure_information {
 /** SMBIOS enclosure information structure type */
 #define SMBIOS_TYPE_ENCLOSURE_INFORMATION 3
 
+/** SMBIOS OEM strings structure type */
+#define SMBIOS_TYPE_OEM_STRINGS 11
+
 /**
  * SMBIOS entry point descriptor
  *