efi_loader: add copyright notice

Some amount of code was moved/derived from efi_variable.c regarding
UEFI secure boot, in particluar in the commit 012c56ac76e1 ("efi_loader:
restructure code for TEE variables").
So add the orignal author's copyright notice.

Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
diff --git a/lib/efi_loader/efi_var_common.c b/lib/efi_loader/efi_var_common.c
index 453cbce5..1c74592 100644
--- a/lib/efi_loader/efi_var_common.c
+++ b/lib/efi_loader/efi_var_common.c
@@ -3,6 +3,7 @@
  * UEFI runtime variable services
  *
  * Copyright (c) 2020, Heinrich Schuchardt <xypron.glpk@gmx.de>
+ * Copyright (c) 2020 Linaro Limited, Author: AKASHI Takahiro
  */
 
 #include <common.h>