macintosh: Use common code to access RTC

Now that the 68k Mac port has adopted the via-pmu driver, the same RTC
code can be shared between m68k and powerpc. Replace duplicated code in
arch/powerpc and arch/m68k with common RTC accessors for Cuda and PMU.

Drop the problematic WARN_ON which was introduced in commit 22db552b50fa
("powerpc/powermac: Fix rtc read/write functions").

Tested-by: Stan Johnson <userm57@yahoo.com>
Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
diff --git a/include/linux/cuda.h b/include/linux/cuda.h
index 056867f..45bfe9d 100644
--- a/include/linux/cuda.h
+++ b/include/linux/cuda.h
@@ -8,6 +8,7 @@
 #ifndef _LINUX_CUDA_H
 #define _LINUX_CUDA_H
 
+#include <linux/rtc.h>
 #include <uapi/linux/cuda.h>
 
 
@@ -16,4 +17,7 @@ extern int cuda_request(struct adb_request *req,
 			void (*done)(struct adb_request *), int nbytes, ...);
 extern void cuda_poll(void);
 
+extern time64_t cuda_get_time(void);
+extern int cuda_set_rtc_time(struct rtc_time *tm);
+
 #endif /* _LINUX_CUDA_H */