Drivers for the mc146818 RTC generally check control registers to
determine whether a value is encoded as binary or as a binary coded
decimal. Setting RTC_ALWAYS_BCD to 1 effectively bypasses these checks
and causes drivers to always expect binary coded decimal values,
regardless of control register values.
This does not seem like a sane default - defaulting to 0 allows the
drivers to check control registers to determine encoding type & allows
the driver to work generically with both binary & BCD encodings. Set
this in mach-generic/mc146818rtc.h such that the generic kernel, or
platforms which don't provide a custom mc146818rtc.h, can have an RTC
driver which works with both encodings.