core: load IPE policy on boot

core: load IPE policy on boot

IPE is a new LSM being introduced in 6.12. Like IMA, it works based on a
policy file that has to be loaded at boot, the earlier the better. So
like IMA, if such a policy is present, load it and activate it.

If there are any .p7b files in /etc/ipe/, load them as policies.
The files have to be inline signed in DER format as per IPE documentation.

For more information on the details of IPE:

https://microsoft.github.io/ipe/