x86/platform/intel-mid: Allocate RTC interrupt for Merrifield

x86/platform/intel-mid: Allocate RTC interrupt for Merrifield

Legacy RTC requires interrupt line 8 to be dedicated for it. On
Intel MID platforms the legacy PIC is absent and in order to make RTC
work we need to allocate interrupt separately.

Current solution brought by commit de1c2540aa4f does it in a wrong place,
and since it's done unconditionally for all x86 devices, some of them,
e.g. PNP based, might get it wrong because they execute the MID specific
code due to x86_platform.legacy.rtc flag being set.

Move intel_mid_legacy_rtc_init() to its own module and call it before x86 RTC
CMOS initialization.

Fixes: de1c2540aa4f ("x86/platform/intel-mid: Enable RTC on Intel Merrifield")
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: "Luis R . Rodriguez" <mcgrof@kernel.org>
Link: http://lkml.kernel.org/r/20170119192425.189899-3-andriy.shevchenko@linux.intel.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>