[PATCH] macintosh: fix via-pmu and via-cuda build errors

[Finn Thain]

On Wed, 6 Apr 2022, Randy Dunlap wrote:

> When CONFIG_RTC_CLASS is not set, rtc_tm_to_time64() is not defined.
> 
> ...
> 
> m68k-linux-ld: drivers/macintosh/via-pmu.o: in function `pmu_set_rtc_time':
> drivers/macintosh/via-pmu.c:1758: undefined reference to `rtc_tm_to_time64'
> m68k-linux-ld: drivers/macintosh/via-cuda.o: in function `cuda_set_rtc_time':
> drivers/macintosh/via-cuda.c:797: undefined reference to `rtc_tm_to_time64'
> 
> ...
> This is a big hammer type of patch. We could possibly do (a) some
> conditional code blocks for RTC_CLASS 

rtc_tm_to_time64() call sites also appear in several other files without 
conditionals:

arch/powerpc/kernel/time.c
arch/powerpc/platforms/8xx/m8xx_setup.c
arch/powerpc/platforms/maple/time.c
arch/powerpc/platforms/powermac/time.c

Why not use mktime64() instead? That seems to be a common pattern for this 
kind of thing (without needing conditional code).