bcm63xx: use generic diag.sh

bcm63xx: use generic diag.sh

This commit removes the target-specific diag.sh script. This way, the
generic one is used for the target, which uses DT-aliases to specify the
LEDs used.

Though generic diag.sh allows to use different LEDs to indicate different
states, this patch just moves the old assignment and does not try to
"improve" the assignment by using additional colors.
However, individual proposals to do so are welcome.

For the few cases where status_led2 was used in old diag.sh, only the
primary LED was migrated.

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>