kmp204x: Add support for the unit LEDs

The unit LEDs are managed by the QRIO CPLD. This patch adds support for
accessing these LEDs in the QRIO.

The LEDs then are set to a correct boot state:
- UNIT-LED is red
- BOOT-LED is on.

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