kunit: tool: Use qboot on QEMU x86_64

As noted in [0], SeaBIOS (QEMU default) makes a mess of the terminal,
qboot does not.

It turns out this is actually useful with kunit.py, since the user is
exposed to this issue if they set --raw_output=all.

qboot is also faster than SeaBIOS, but it's is marginal for this
usecase.

[0] https://lore.kernel.org/all/CA+i-1C0wYb-gZ8Mwh3WSVpbk-LF-Uo+njVbASJPe1WXDURoV7A@mail.gmail.com/

Both SeaBIOS and qboot are x86-specific.

Link: https://lore.kernel.org/r/20250124-kunit-qboot-v1-1-815e4d4c6f7c@google.com


Signed-off-by: Brendan Jackman <jackmanb@google.com>
Reviewed-by: David Gow <davidgow@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>