sun4u: rename apb variables and constants

In order to reflect the previous change of TYPE_APB to TYPE_SABRE, update
the corresponding variable names to keep the terminology consistent.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Acked-by: Artyom Tarasenko <atar4qemu@gmail.com>