Previously, the partition table definition was defined inside an assembler.
This has an issue though: The partitions and filesystems are needed at several
other places, e.g. grub2 stage and fstab stage. As the partition table was
basically hardcoded, this didn't matter - we could just use constants
in these stages. Not ideal but it worked.
This commit changes the behaviour: A partition table is firstly created and
then it's passed to the assembler function where complete assembler options
are created out of it.
To make this change as small as possible, osbuild.QEMUAssemblerOptions type
is used to encode the partition table for now.
Signed-off-by: Ondřej Budai <ondrej@budai.cz>