abstractcs.relaxedpriv: Clarify the description (#765)

* abstractcs.relaxedpriv: Clarify the description

Changed the wording in the description of "abstractcs.relaxedpriv"
field in order to make the meaning of that field clear:

- full permissions --> full permission checks
- relaxed permissions --> relaxed permission checks

The original wording may have suggested the opposite meaning.

* Updated xml/dm_registers.xml per suggestion - added <value> tags

Co-authored-by: Tim Newsome <tim@sifive.com>
Signed-off-by: Jan Matyas <50193733+JanMatCodasip@users.noreply.github.com>

Signed-off-by: Jan Matyas <50193733+JanMatCodasip@users.noreply.github.com>
Co-authored-by: Tim Newsome <tim@sifive.com>