board: em_starter_kit: add default config for em7d in version 22

* arc MPUv2 is only available in em7d em starterkit version 22.
  Add a default config for this to simply the config.

* The change of board version in menuconfig, e.g, version 23 to
  v22, will not cause other options depending on board version
  change automatically, users still need to change these options
  manually. This is another reason to need a new default config file.

Signed-off-by: Wayne Ren <wei.ren@synopsys.com>