lance: move TYPE_LANCE and SysBusPCNetState from lance.c to lance.h

lance: move TYPE_LANCE and SysBusPCNetState from lance.c to lance.h

This enables them to be used outside of lance.c. We also update the comment to
refer to the SPARC32 lance device rather than the AMD PCNet-II device (of which
lance is a register-compatible subset).

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
CC: Jason Wang <jasowang@redhat.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Tested-by: Philippe Mathieu-Daudé <f4bug@amsat.org>