Avoid cyclic dependencies in class_header.
Avoid cyclic dependencies in class_header.

Don't include uhdm.h, which in turn includes
everything, cyclic-including the current header - this
will result in undefined classes depending on which
of these are included first.

Instead, just include the header we need (the base
class of what we're extending).

Signed-off-by: Henner Zeller <259ad50fabbfd39355f36ecd6c0afca541ea66ef@acm.org>

chipsalliance/UHDM,chipsalliance/UHDM,chipsalliance/UHDM