package/python-pycryptodomex: add host variant

Adding a host variant will allow to replace host-python-pycrypto by
host-python-pycryptodomex for the crda and optee-os packages.

From [1]:
"PyCryptodome is a fork of PyCrypto, which is not maintained any more
(the last release dates back to 2013 [2]). It exposes almost the same
API, but there are a few incompatibilities [3]."

[1] https://github.com/OP-TEE/optee_os/commit/90ad2450436fdd9fc0d28a3f92f3fbcfd89a38f0
[2] https://pypi.org/project/pycrypto/#history
[3] https://pycryptodome.readthedocs.io/en/latest/src/vs_pycrypto.html



Signed-off-by: Romain Naour <romain.naour@gmail.com>
Cc: James Hilliard <james.hilliard1@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>