hw/isa/vt82c686: Resolve chip-specific realize methods

hw/isa/vt82c686: Resolve chip-specific realize methods

The object creation now happens in chip-specific init methods which
allows the realize methods to be consolidated into one method. Shifting
the logic into the init methods has the addidional advantage that the
parent object's init methods are called implicitly - like constructors
in object-oriented languages.

Signed-off-by: Bernhard Beschow <shentey@gmail.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20220901114127.53914-2-shentey@gmail.com>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>