x86/platform/intel-mid: Remove per platform code

After custom TSC calibration gone, there is no more reason to have
custom platform code for each of Intel MID.

Thus, remove it for good.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Pavel Tatashin <pasha.tatashin@oracle.com>
Link: https://lkml.kernel.org/r/20180629193113.84425-7-andriy.shevchenko@linux.intel.com