roms: lift "edk2-funcs.sh" from "tests/uefi-test-tools/build.sh"

roms: lift "edk2-funcs.sh" from "tests/uefi-test-tools/build.sh"

Extract the dense logic for architecture and toolchain massaging from
"tests/uefi-test-tools/build.sh", to a set of small functions. We'll reuse
these functions for building full platform firmware images.

Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Tested-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>