The memory domain APIs document that overlapping regions are
not allowed, check for this unconditionally.
Cleanup assertion error messages. Use __ASSERT_NO_MSG for
blindingly obvious NULL checks.
We now have a `check_add_partition()` function to perform
all the necessary sanity checks on adding a partition to a
domain. This returns true or false, which will help later
when we implement #24609
Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>