oscplot: use the same marker labels in the plot as in the GUI list

Note that we currently only allow strings that are five characters in
length (plus the null termination) since "Image" is the longest label
we're using now.

Signed-off-by: Tim Harder <timothy.harder@analog.com>
profiles: tweak various daq2 test profile values

Signed-off-by: Tim Harder <timothy.harder@analog.com>