tune-cortexa73: Introduce cortexa73-crypto tune

The crypto extension is optional for the Cortex-A73 processor, so we
shouldn't enable the crypto by default for the cortexa73 tune.
Introduce the cortexa73-crypto for the processors which do have
the cryptography unit.

Signed-off-by: Kevin Hao <kexin.hao@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>