Currently the vDSO tests are built only on x86 platforms and cannot be
cross compiled.

Enable vDSO TARGET for all the platforms.

Future patches will extend the tests.

Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>