hw/isa/vt82c686: Create rtc-time alias in boards instead

hw/isa/vt82c686: Create rtc-time alias in boards instead

According to good QOM practice, an object should only deal with objects
of its own sub tree. Having devices create an alias on the machine
object doesn't respect this good practice. To resolve this, create the
alias in the machine's code.

Signed-off-by: Bernhard Beschow <shentey@gmail.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Acked-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Message-Id: <20220901114127.53914-14-shentey@gmail.com>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>