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/Kconfig b/lib/efi_loader/Kconfig
index 1cfa24f..aad37b7 100644
--- a/lib/efi_loader/Kconfig
+++ b/lib/efi_loader/Kconfig
@@ -164,4 +164,13 @@
 	  it is signed with a trusted key. To do that, you need to install,
 	  at least, PK, KEK and db.
 
+config EFI_MM_COMM_TEE
+	bool "UEFI variables storage service via OP-TEE"
+	depends on OPTEE
+	default n
+	help
+	  If OP-TEE is present and running StandAloneMM, dispatch all UEFI variable
+	  related operations to that. The application will verify, authenticate and
+	  store the variables on an RPMB.
+
 endif