arch/x86: multiboot: add bootargs support

Add bootargs support for multiboot. This
implements get_bootargs() when multiboot and
bootargs are selected in config.

Signed-off-by: Jakub Michalski <jmichalski@internships.antmicro.com>
Signed-off-by: Filip Kokosinski <fkokosinski@antmicro.com>
6 files changed