SMBIOS: Introduce struct for SMBIOS table header

All SMBIOS `type X` tables start with the same 4-byte header. Add a
struct definition for it, and use it where applicable. The union is
temporary and allows doing the necessary changes in smaller commits.

Change-Id: Ibd9a80010f83fd7ebefc014b981d430f5723808c
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/55906
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Tim Wawrzynczak <twawrzynczak@chromium.org>

src/drivers/wifi/generic/smbios.c

@@ -10,9 +10,14 @@
 static int smbios_write_intel_wifi(struct device *dev, int *handle, unsigned long *current)
 {
 	struct smbios_type_intel_wifi {
-		u8 type;
-		u8 length;
-		u16 handle;
+		union {
+			struct {
+				u8 type;
+				u8 length;
+				u16 handle;
+			};
+			struct smbios_header header;
+		};
 		u8 str;
 		u8 eos[2];
 	} __packed;