build(mt8195): Add CROS_WIDEVINE_SMC variant

We will enable the OPTEE_ALLOW_SMC_LOAD and CROS_WIDEVINE_SMC on our
platform at the same time.

Change-Id: I9ee30bd5b5a49d952a4486f9cec74d6372104660
Signed-off-by: Yi Chou <yich@google.com>
diff --git a/tf_config/mt8195-opteed-smc-load b/tf_config/mt8195-opteed-smc-load
index dd0d443..ab627e8 100644
--- a/tf_config/mt8195-opteed-smc-load
+++ b/tf_config/mt8195-opteed-smc-load
@@ -1,4 +1,5 @@
 COREBOOT=1
+CROS_WIDEVINE_SMC=1
 CROSS_COMPILE=aarch64-none-elf-
 OPTEE_ALLOW_SMC_LOAD=1
 PLAT=mt8195