image_types: Fix reproducible builds for initramfs and UKI img

I've encountered issues reproducing initramfs and UKI image builds,
which will be fixed with this patch.

1. initramfs
There's a symbolic link to /sbin/init, which is appended to the cpio archive after creation.
The links timestamp needs to be static and the cpio append command needs the '--reproducible' flag to produce deterministic outcomes.

2. Unified Kernel Image
'--preserve-dates' is required for a static 'Time/Date' entry.
I've added '--enable-deterministic-archives' although in my case this
didn't change anything.

(From OE-Core rev: fd027729bafb4e085ba0949e38e724f3a8cad102)

Signed-off-by: Frieder Paape <frieder@konvera.io>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

scripts/lib/wic/plugins/source/bootimg-efi.py

@@ -351,6 +351,8 @@ class BootimgEFIPlugin(SourcePlugin):
 
                 # https://www.freedesktop.org/software/systemd/man/systemd-stub.html
                 objcopy_cmd = "%s-objcopy" % target_sys
+                objcopy_cmd += " --enable-deterministic-archives"
+                objcopy_cmd += " --preserve-dates"
                 objcopy_cmd += " --add-section .osrel=%s/usr/lib/os-release" % staging_dir_host
                 objcopy_cmd += " --change-section-vma .osrel=0x20000"
                 objcopy_cmd += " --add-section .cmdline=%s" % cmdline.name