boards: m5stack: cores3: Add CoreS3 SE variant

Add `se` variant to support the low-cost CoreS3 SE.

- Add configuration files
  Add `m5stack_cores3_procpu_se(.dts|.yaml|defconfig)` files.
  Reorganize dts files to split common parts.

- Update .yaml file
  Add gpio, can, counter, entropy, pwm, and pinmux to the supported
  feature group. Remove the `ignore_tags:` section.

- Update documents
  Add and modify information about CoreS3 SE.
  Add more description about sysbuild.

Signed-off-by: TOKITA Hiroshi <tokita.hiroshi@gmail.com>