pkcs11: use the same initialization code for provider

pkcs11: use the same initialization code for provider

This makes the pkcs11-provider code use the thread-safe module
initialization code introduced in commit
aa5f15a872e62e54abe58624ee393e68d1faf689. As the mechanism works over
p11-kit managed modules, this switches the "path" config option to
using PKCS#11 URI, through the "url" keyword.

Signed-off-by: Daiki Ueno <ueno@gnu.org>