Explicitly cast some switch parameters to enum

Explicitly cast some switch parameters to enum

This patch is not trying to fix every switch, just the ones I worked
with last time, because some of these were especially unreadable.
Covers enums virDomainGraphicsType and virDomainChrType (where
applicable).

Also sort its cases by their value.

Signed-off-by: Martin Kletzander <mkletzan@redhat.com>