efi_loader: Implement EFI variable handling via OP-TEE

In OP-TEE we can run EDK2's StandAloneMM on a secure partition.
StandAloneMM is responsible for the UEFI variable support. In
combination with OP-TEE and it's U-Boot supplicant, variables are
authenticated/validated in secure world and stored on an RPMB partition.

So let's add a new config option in U-Boot implementing the necessary
calls to OP-TEE for the variable management.

Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Signed-off-by: Pipat Methavanitpong <pipat1010@gmail.com>
Signed-off-by: Sughosh Ganu <sughosh.ganu@linaro.org>
Reviewed-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
diff --git a/lib/efi_loader/Makefile b/lib/efi_loader/Makefile
index 84d61df..57c7e66 100644
--- a/lib/efi_loader/Makefile
+++ b/lib/efi_loader/Makefile
@@ -35,7 +35,11 @@
 obj-y += efi_runtime.o
 obj-y += efi_setup.o
 obj-$(CONFIG_EFI_UNICODE_COLLATION_PROTOCOL2) += efi_unicode_collation.o
+ifeq ($(CONFIG_EFI_MM_COMM_TEE),y)
+obj-y += efi_variable_tee.o
+else
 obj-y += efi_variable.o
+endif
 obj-y += efi_watchdog.o
 obj-$(CONFIG_LCD) += efi_gop.o
 obj-$(CONFIG_DM_VIDEO) += efi_gop.o