integrity: provide a function to load x509 certificate from the kernel

Provide the function to load x509 certificates from the kernel into the
integrity kernel keyring.

Changes in v2:
* configuration option removed
* function declared as '__init'

Signed-off-by: Dmitry Kasatkin <d.kasatkin@samsung.com>
Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>

diff --cc security/integrity/digsig.c
Simple merge

diff --cc security/integrity/integrity.h
Simple merge