[smbios] Expose board serial number as ${board-serial}

With blade servers, the chassis serial number (exposed via ${serial})
may not be unique.  Expose ${board-serial} as a named setting to
provide easy access to a more meaningful serial number.

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

src/include/ipxe/smbios.h

 /** SMBIOS system information structure type */
 #define SMBIOS_TYPE_SYSTEM_INFORMATION 1
 
+/** SMBIOS base board information structure */
+struct smbios_base_board_information {
+	/** SMBIOS structure header */
+	struct smbios_header header;
+	/** Manufacturer string */
+	uint8_t manufacturer;
+	/** Product string */
+	uint8_t product;
+	/** Version string */
+	uint8_t version;
+	/** Serial number string */
+	uint8_t serial;
+} __attribute__ (( packed ));
+
+/** SMBIOS base board information structure type */
+#define SMBIOS_TYPE_BASE_BOARD_INFORMATION 2
+
 /** SMBIOS enclosure information structure */
 struct smbios_enclosure_information {
 	/** SMBIOS structure header */

src/interface/smbios/smbios_settings.c

 	.type = &setting_type_string,
 	.scope = &smbios_settings_scope,
 };
+
+/** Board serial number setting (may differ from chassis serial number) */
+const struct setting board_serial_setting __setting ( SETTING_HOST_EXTRA,
+						      board_serial ) = {
+	.name = "board-serial",
+	.description = "Base board serial",
+	.tag = SMBIOS_STRING_TAG ( SMBIOS_TYPE_BASE_BOARD_INFORMATION,
+				   struct smbios_base_board_information,
+				   serial ),
+	.type = &setting_type_string,
+	.scope = &smbios_settings_scope,
+};