samples: logging/syst: expand to doing v1/v2 immediate/deferred

This expands the sample to do both v1 and v2, and both immediate
and deferred modes for each logging verion. This is to make sure
MIPI Sys-T output is not broken for all combinations. Default is
v2/immediate using prj.conf. Deferred mode is enabled via
overlay.

Also add qemu_x86 as an allowed platform as the samples are
working there too.

Signed-off-by: Daniel Leung <daniel.leung@intel.com>