kmp204x: selftest/factory test pin support

kmp204x: selftest/factory test pin support

This patch defines the post_hotkeys_pressed() function that is used for:
- triggering POST memory regions test
- starting the test application through the checktestboot command in
  a script by setting the active bank to testbank

The post_hotkeys_pressed return the state of the SELFTEST pin.

The patch moves from the complete POST-memory test that is too long in
its SLOW version for our production HW test procedure to the much shorter
POST-memory-regions test.

Finally, the unused #defines for the not so relevant mtest command are
removed.

Signed-off-by: Stefan Bigler <stefan.bigler@keymile.com>
Signed-off-by: Valentin Longchamp <valentin.longchamp@keymile.com>