Make lsinitrd usable for images made with Debian mkinitramfs

Make lsinitrd usable for images made with Debian mkinitramfs

Debian mkinitramfs does not create the file 'early_cpio', so detection
of additional cpio images fails and only the first cpio is listed.

I checked some Arch and Gentoo initramfs files and these didn't have
'early_cpio' either, but they also have only one cpio part.

Fix this so that if check for 'early_cpio' fails, check if firmware
files ('/kernel/*/microcode/*.bin') exist.

Signed-off-by: Topi Miettinen <toiwoton@gmail.com>