x86/platform/intel-mid: Add Power Management Unit driver

Add Power Management Unit driver to handle power states of South Complex
devices on Intel Tangier. In the future it might be expanded to cover North
Complex devices as well.

With this driver the power state of the host controllers such as SPI, I2C,
UART, eMMC, and DMA would be managed.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: David Cohen <david.a.cohen@linux.intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mika Westerberg <mika.westerberg@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-pci@vger.kernel.org
Link: http://lkml.kernel.org/r/1465928985-12113-1-git-send-email-andriy.shevchenko@linux.intel.com
[ Minor readability edits. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>