PL2: Explicity declare 64 bit apps support

* Silences the follwoing build warning:
build/make/core/board_config.mk:180: warning: Building a 32-bit-app-only product on a 64-bit device. If this is intentional, set TARGET_SUPPORTS_64_BIT_APPS := false

BoardConfig.mk

@@ -57,6 +57,7 @@ TARGET_PREBUILT_KERNEL := $(LOCAL_PATH)/prebuilt/Image.gz-dtb
 # Platform
 TARGET_BOARD_PLATFORM := sdm660
 TARGET_BOARD_PLATFORM_GPU := qcom-adreno508
+TARGET_SUPPORTS_64_BIT_APPS := true
 
 # Encryption
 #PLATFORM_VERSION := 16.1.0