selftests/sgx: Add "test_encl.elf" to TEST_FILES

The "test_encl.elf" file used by test_sgx is not installed in
INSTALL_PATH. Attempting to execute test_sgx causes false negative:

"
enclave executable open(): No such file or directory
main.c:188:unclobbered_vdso:Failed to load the test enclave.
"

Add "test_encl.elf" to TEST_FILES so that it will be installed.

Fixes: 2adcba79 ("selftests/x86: Add a selftest for SGX")
Signed-off-by: NYi Lai <yi1.lai@intel.com>
Reviewed-by: NJarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: NShuah Khan <skhan@linuxfoundation.org>

tools/testing/selftests/sgx/Makefile

@@ -17,6 +17,7 @@ ENCL_CFLAGS := -Wall -Werror -static -nostdlib -nostartfiles -fPIC \
 	       -fno-stack-protector -mrdrnd $(INCLUDES)
 
 TEST_CUSTOM_PROGS := $(OUTPUT)/test_sgx
+TEST_FILES := $(OUTPUT)/test_encl.elf
 
 ifeq ($(CAN_BUILD_X86_64), 1)
 all: $(TEST_CUSTOM_PROGS) $(OUTPUT)/test_encl.elf