efi/peimage: Provide an implementation of load_image, start_image, unload_image

efi/peimage: Provide an implementation of load_image, start_image, unload_image

The code consumes a PE-COFF image loaded into memory. The functions

* check validity of header
* copy the sections
* relocate the code
* set memory attributes
* invalidate the instruction cache
* execute the image
* return to caller

Caveats:

- We do not always check for over and underflows, but at the
  point we reach this loader, the file has been verified by
  shim already, so this is not much of a concern.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Signed-off-by: Julian Andres Klode <julian.klode@canonical.com>
Signed-off-by: Mate Kukri <mate.kukri@canonical.com>
Gbp-Pq: Topic secure-boot
Gbp-Pq: Name efi-peimage.patch