x86: rtc: don't register a platform RTC device for Intel MID platforms

x86: rtc: don't register a platform RTC device for Intel MID platforms

Intel MID x86 platforms have a memory mapped virtual RTC instead.  No MID
platform have the default ports (and accessing them may do weird stuff)

Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Cc: Feng Tang <feng.tang@intel.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>