package/libp11: new package

package/libp11: new package

Library for using PKCS#11, which includes an engine for OpenSSL that
lets it use PKCS#11 modules.  Which is really what this package is
about, not that libp11 library itself, which has no users outside the
of OpenSSL engine.

If p11-kit is enabled, configure the engine to use that as the default
PKCS#11 module.  That module is a sort of multiplexer that allows
multiple modules to be used at once, so it makes sense to use it even
if there are other modules present, e.g. softhsm2, nssckbi,
pkcs11-proxy, ykcs11, etc.

A host package is created too, with a host configuration option.
Since this a dynamically loaded module, there is no build time reason
to select it from a host package.  It could be used by host openssl,
to allow host rauc to sign a software update bundle using a key from a
HSM with a PKCS#11 interface.

Signed-off-by: Trent Piepho <tpiepho@impinj.com>
Tested-by: Frank Hunleth <fhunleth@troodon-software.com>
[Thomas:
 - add entry in DEVELOPERS file
 - add missing !BR2_STATIC_LIBS dependency
 - fix license information, as noticed by Frank Hunleth
 - add missing dependency on host-pkgconf, needed by the configure
   script to detect openssl
 - explicitly pass --with-enginesdir as the value returned by
   pkg-config is incorrectly prefixed by the sysroot]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>