efistub/smbios: Simplify SMBIOS enumeration API

Update the efi_get_smbios_string() macro to take a pointer to the entire
record struct rather than the header. This removes the need to pass the
type explicitly, as it can be inferred from the typed pointer. Also,
drop 'type' from the prototype of __efi_get_smbios_string(), as it is
never referenced.

Signed-off-by: Ard Biesheuvel <[e-mail]>

drivers/firmware/efi/libstub/arm64.c

···
 		static char const emag[] = "eMAG";
 
 	default:
-		version = efi_get_smbios_string(&record->header, 4,
-						processor_version);
+		version = efi_get_smbios_string(record, processor_version);
 		if (!version || (strncmp(version, altra, sizeof(altra) - 1) &&
 				 strncmp(version, emag, sizeof(emag) - 1)))
 			break;

drivers/firmware/efi/libstub/efistub.h

···
 	u16				thread_enabled;
 };
 
-#define efi_get_smbios_string(__record, __type, __name) ({		\
-	int off = offsetof(struct efi_smbios_type ## __type ## _record,	\
-			   __name);					\
-	__efi_get_smbios_string((__record), __type, off);		\
+#define efi_get_smbios_string(__record, __field) ({			\
+	__typeof__(__record) __rec = __record;				\
+	__efi_get_smbios_string(&__rec->header, &__rec->__field);	\
 })
 
 const u8 *__efi_get_smbios_string(const struct efi_smbios_record *record,
-				  u8 type, int offset);
+				  const u8 *offset);
 
 void efi_remap_image(unsigned long image_base, unsigned alloc_size,
 		     unsigned long code_size);

drivers/firmware/efi/libstub/smbios.c

···
 }
 
 const u8 *__efi_get_smbios_string(const struct efi_smbios_record *record,
-				  u8 type, int offset)
+				  const u8 *offset)
 {
 	const u8 *strtable;
 
···
 		return NULL;
 
 	strtable = (u8 *)record + record->length;
-	for (int i = 1; i < ((u8 *)record)[offset]; i++) {
+	for (int i = 1; i < *offset; i++) {
 		int len = strlen(strtable);
 
 		if (!len)