uefi: When adding headers set the header size to 4k
uefi: When adding headers set the header size to 4k

This solves issues with implementations that require 4k alignment
of pages in BIOS which is seen on certain architectures.

The UEFI spec prescribes that the "minimum" size is the size of
the EFI header but that this may be increased up to larger sizes
due to extended header entries.

hughsie/fwupd,fwupd/fwupd,fwupd/fwupd,vathpela/fwupd,hughsie/fwupd,hughsie/fwupd,vathpela/fwupd,vathpela/fwupd,fwupd/fwupd,vathpela/fwupd,fwupd/fwupd,hughsie/fwupd