samples: drivers: mbox: fix adp_xc7k/ae350 configuration and overlay

This commit fixes the following issues for adp_xc7k/ae350
  1. Incorrect copyright due to copy-paste error
  2. Separate RAM region for the host and remote clusters
  3. Allocate hart 0 for host and hart 1 for remote cluster
  4. Use mbox channel 9, 10 for the sample, leaving channel/irq source
     1 ~ 8 for ae350 8-core IPI

Signed-off-by: Jimmy Zheng <jimmyzhe@andestech.com>