viridian: separate time related enlightenment implementations...

viridian: separate time related enlightenment implementations...

...into new 'time' module.

This patch reduces the size of the main viridian source module by
moving time related enlightenments into their own source module. This is
done in anticipation of implementation of more such enightenments and
a desire to not further lengthen the main source module when this work
is done.

While moving the code:

- Move the declaration of HV_REFERENCE_TSC_PAGE from the header file into
  the new source module, since it is only used there.
- Clean up a bool_t.

Signed-off-by: Paul Durrant <paul.durrant@citrix.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>