flask: unify {get, set}vcpucontext permissions

flask: unify {get, set}vcpucontext permissions

These permissions were initially split because they were in separate
domctls, but this split is very unlikely to actually provide security
benefits: it would require a carefully contrived situation for a domain
to both need access to one type of CPU register and also need to be
prohibited from accessing another type.

Signed-off-by: Daniel De Graaf <dgdegra@tycho.nsa.gov>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Reviewed-by: Doug Goldstein <cardoe@cardoe.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>