tools/bootconfig: Quote CPU masks containing comma-separated words

ftrace2bconf.sh writes the CPU mask without quotes. For a mask selecting
CPUs 0 and 32, the output is:

  ftrace.cpumask = 00000001,00000001

Bootconfig reads the two comma-separated words as separate array values.
When bconf2ftrace.sh applies the saved settings, it writes those values
on separate lines instead of restoring the original CPU mask.

Quote the mask so the commas remain part of a single value.

Link: https://lore.kernel.org/all/20261019120332.553567-1-edumucelli@gmail.com/

Fixes: 2b86062a34a8 ("tools/bootconfig: Add a script to generates bootconfig from ftrace")
Signed-off-by: Eduardo Mucelli Rezende Oliveira <edumucelli@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>