[efi] Discard .pci_devlist.* sections for EFI images

As per https://github.com/ipxe/ipxe/pull/313#issuecomment-816018398,
these sections are not required for EFI execution.  Discard them to
avoid implementation-defined alignment malforming binaries.

Signed-off-by: Marvin Häuser <mhaeuser@posteo.de>