target/x86: add grub2-bios-setup to DEFAULT_PACKAGES
With the commit
5876d6a62fc0ae5799e7d9c896356f75c99a6f0a the command under
`/usr/sbin/grub-bios-setup` has been moved to its own package named
`grub-bios-setup`.
The script `81_upgrade_bootloader` under `/lib/preinit` is used by all
x86 targets to update the bootloader. The script is using the command
`grub-bios-setup` for this.
I get the following output at the first boot after the upgrade.
`/etc/preinit: line 9: /usr/sbin/grub-bios-setup: not found`.
To fix this, the DEFAULT_PACKAGES dependency is extended by the entry
`grub2-bios-setup` so that the missing command is installed again.
Signed-off-by: Florian Eckert <fe@dev.tdt.de>