efi_loader: function to get GUID for variable name

In multiple places we need the default GUID matching a variable name.
The patch provides a library function. For secure boot related variables
like 'PK', 'KEK', 'db' a lookup table is used. For all other variable
names EFI_GLOBAL_VARIABLE is returned.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
diff --git a/include/efi_variable.h b/include/efi_variable.h
index 8f666b2..03a3ecb 100644
--- a/include/efi_variable.h
+++ b/include/efi_variable.h
@@ -257,6 +257,14 @@
 					     const efi_guid_t *guid);
 
 /**
+ * efi_auth_var_get_guid() - get the predefined GUID for a variable name
+ *
+ * @name:	name of UEFI variable
+ * Return:	guid of UEFI variable
+ */
+const efi_guid_t *efi_auth_var_get_guid(const u16 *name);
+
+/**
  * efi_get_next_variable_name_mem() - Runtime common code across efi variable
  *                                    implementations for GetNextVariable()
  *                                    from the cached memory copy