macintosh: via-pmu and via-cuda need RTC_LIB

macintosh: via-pmu and via-cuda need RTC_LIB

Fix build when RTC_LIB is not set/enabled.
Eliminates these build errors:

m68k-linux-ld: drivers/macintosh/via-pmu.o: in function `pmu_set_rtc_time':
drivers/macintosh/via-pmu.c:1769: 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'

Fixes: 0792a2c8e0bb ("macintosh: Use common code to access RTC")
Reported-by: kernel test robot <lkp@intel.com>
Suggested-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220410161035.592-1-rdunlap@infradead.org