powerpc: Remove stale function prototypes from setup.h

I noticed a couple of function prototypes for functions that
no longer exist. Remove them.
Signed-off-by: NAnton Blanchard <anton@samba.org>
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/include/asm/setup.h

@@ -13,10 +13,6 @@ extern unsigned long long memory_limit;
 extern unsigned long klimit;
 extern void *zalloc_maybe_bootmem(size_t size, gfp_t mask);
 
-extern void via_cuda_init(void);
-extern void read_rtc_time(void);
-extern void pmac_find_display(void);
-
 struct device_node;
 extern void note_scsi_host(struct device_node *, void *);