cryptsetup: add native pkcs#11 support to cryptsetup

This adds a new crypttab option for volumes "pkcs11-uri=" which takes a
PKCS#11 URI. When used the key stored in the line's key file is
decrypted with the private key the PKCS#11 URI indiciates.

This means any smartcard that can store private RSA keys is usable for
unlocking LUKS devices.