Docs: Update descriptions in isolation doc

There are out-of-date descriptions, update them:

- Involve rule I7.
- Update the default system map descriptions.
- Other tiny adjustments.

Signed-off-by: Ken Liu <Ken.Liu@arm.com>
Change-Id: Id5b3f8f556ecbcc03e24da36e71f0fe51249ecbc
1 file changed