Power guest secure boot with key management: userspace portion

Covering the userspace portion (secvarctl)

Feature:

This feature comprises PowerVM LPAR guest OS kernel verification to extend the chain of trust from partition firmware to the OS kernel and includes key management. GRUB and the host OS kernel are signed with 2 separate public key pairs. Partition firmware includes the the public verification key for GRUB in its build and uses it to verify GRUB. GRUB includes the public verification key for the OS kernel in its build and uses it to verify the OS kernel image

Test case:

If secure boot is switched off, any GRUB and kernel boots.
If secure boot is switched on:
  - Properly signed GRUB boots.
  - Improperly signed GRUB does not boot.
  - Tampered signed GRUB does not boot.
  - Properly signed kernels boot.
  - Improperly signed kernels do not boot.
  - Tampered signed kernels do not boot.
TPM PCRs are extended roughly following the TCG PC Client and UEFI specs as they apply to POWER.