[MIPS] Switch from to_tm to rtc_time_to_tm

This replaces the MIPS-specific to_tm function with the generic
rtc_time_to_tm function.  The big difference between the two functions is
that rtc_time_to_tm uses epoch 70 while to_tm uses 1970, so the result of
rtc_time_to_tm needs to be fixed up.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/Kconfig

@@ -3,6 +3,7 @@ config MIPS
 	default y
 	# Horrible source of confusion.  Die, die, die ...
 	select EMBEDDED
+	select RTC_LIB
 
 mainmenu "Linux/MIPS Kernel Configuration"