Bluetooth: SMP: Use AES-CMAC library API

Bluetooth: SMP: Use AES-CMAC library API

Now that AES-CMAC has a library API, convert net/bluetooth/smp.c to use
it instead of the "cmac(aes)" crypto_shash.  Since the library API
doesn't require dynamic memory allocation, we no longer need to pass a
crypto_shash object down the call stack and can simply allocate the
aes_cmac_key on the stack in smp_aes_cmac() (renamed from aes_cmac()).

The result is simpler and faster code that no longer relies on the
error-prone loading of algorithms by name.

Note that the maximum stack usage actually decreases slightly, despite
the expanded AES key being moved to the stack.  This is because the old
code called crypto_shash_tfm_digest(), which allocates 384 bytes on the
stack for a maximally-sized hash descriptor for any algorithm.  The new
code instead declares a 288-byte aes_cmac_key, then calls aes_cmac()
which declares a 32-byte aes_cmac_ctx.  Since 288 + 32 < 384, the
maximum stack usage decreases.  I.e. the entire expanded AES key easily
fits in the space that the generic crypto API was wasting before.

I didn't add zeroization of the aes_cmac_key, since smp_aes_cmac()
already copies the raw key to the stack without zeroizing it.

Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Eric Biggers <ebiggers@kernel.org>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>