sun4m: remove include/hw/sparc/sun4m.h and all references to it

With the previous commit there is now nothing left in sun4m.h so it can be
removed, along with all remaining references to it.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Acked-by: Artyom Tarasenko <atar4qemu@gmail.com>