crypto: doc - optimize compilation

The :functions: definition allows the specification of multiple
function references which prevents parsing the header file multiple
times.

Reported-by: Jani Nikula <jani.nikula@linux.intel.com>
Signed-off-by: Stephan Mueller <smueller@chronox.de>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

crypto: doc - convert crypto API documentation to Sphinx

With the conversion of the kernel crypto API DocBook to Sphinx, the
monolithic document is broken up into individual documents. The
documentation is unchanged with the exception of a slight reordering to
keep the individual document parts self-contained.

Signed-off-by: Stephan Mueller <smueller@chronox.de>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>