cryptodev: fix checks related to device id

cryptodev: fix checks related to device id

Each cryptodev are indexed with dev_id in the global rte_crypto_devices
variable. nb_devs is incremented / decremented each time a cryptodev is
created / deleted. The goal of nb_devs was to prevent the user to get an
invalid dev_id.

Let's imagine DPDK has configured N cryptodevs. If the cryptodev=1 is
removed at runtime, the latest cryptodev N cannot be accessible, because
nb_devs=N-1 with the current implementaion.

In order to prevent this kind of behavior, let's remove the check with
nb_devs and iterate in all the rte_crypto_devices elements: if data is
not NULL, that means a valid cryptodev is available.

Also, remove max_devs field and use RTE_CRYPTO_MAX_DEVS in order to
unify the code.

Fixes: d11b0f30df88 ("cryptodev: introduce API and framework for crypto devices")
Cc: stable@dpdk.org
Signed-off-by: Julien Meunier <julien.meunier@nokia.com>
Acked-by: Akhil Goyal <akhil.goyal@nxp.com>