conf: Use unsigned long long for timer frequency

conf: Use unsigned long long for timer frequency

Although the code in qemuProcessStartValidateTSC works as if the
timer frequency was already unsigned long long (by using an appropriate
temporary variable), the virDomainTimerDef structure actually defines
frequency as unsigned long, which is not guaranteed to be 64b.

Fixes support for frequencies higher than 2^32 - 1 on 32b systems.

Signed-off-by: Jiri Denemark <jdenemar@redhat.com>
Reviewed-by: Martin Kletzander <mkletzan@redhat.com>