x86/platform/intel-mid: Drop unused __intel_mid_cpu_chip and Co.

Since there is no more user of this global variable and associated custom API,
we may safely drop this legacy reinvented a wheel from the kernel sources.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>