baremetal-helloworld: Enable x86 and x86-64 ports

- The qemux86 port for helloworld-baremetal builds in the standard way, however,
  it uses NASM syntax for the startup code, hence we include a dependency to
  nasm-native, QEMU forces us to use an ELF file rather than a bin file to boot
  from this architecture using the -kernel parameter.

- QEMU refuses to boot using the -kernel parameter for files containing an ELF64
  header [1], instead, it requires a multiboot2 compatible image.

  We could create an image that contains a multiboot2 header by piggybacking
  into grub2-native, specifically grub-mkrescue, but it requires some extra
  runtime dependencies (xorriso which is currently part of meta-oe), and assumes
  a grub installation exists on the host.

  Due to host contamination and dependency complications, we dont rely on grub2,
  but rather do this process manually instead, the x86-64 port contains a stage1
  bootloader, stage2 bootloader and a 64 bit baremetal app (multiboot2
  compatible), booting into real (16 bit), protected (32 bit) and long (64 bit)
  modes, eventually running the helloworld-baremetal app. This is the reason why
  we need the code changes to use a separate Makefile, and create an image
  specifically for qemux86-64.

$ runqemu nographic
Booting from ROM..
Hello OpenEmbedded on x86!

$ runqemu nographic
Starting Stage 1 Bootloader
Loading Stage 2 Bootloader
Stage 2 Loaded.
Jumping to Stage2 Bootloader
In Stage 2
Done

Hello OpenEmbedded on x86-64!

[1] https://gitlab.com/qemu-project/qemu/-/blob/v7.2.0/hw/i386/multiboot.c#L199



Signed-off-by: Alejandro Enedino Hernandez Samaniego <alejandro@enedino.org>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>