platform:x86: add Intel P-Unit mailbox IPC driver

This driver provides support for P-Unit mailbox IPC on Intel platforms.
The heart of the P-Unit is the Foxton microcontroller and its firmware,
which provide mailbox interface for power management usage.

Signed-off-by: Qipeng Zha <qipeng.zha@intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Darren Hart <dvhart@linux.intel.com>
diff --git a/drivers/platform/x86/Kconfig b/drivers/platform/x86/Kconfig
index 1089eaa..148ff88 100644
--- a/drivers/platform/x86/Kconfig
+++ b/drivers/platform/x86/Kconfig
@@ -944,4 +944,10 @@
 	depends on ACPI && INPUT
 	---help---
 	  This driver handles the power/home/volume buttons on the Microsoft Surface Pro 3 tablet.
+
+config INTEL_PUNIT_IPC
+	tristate "Intel P-Unit IPC Driver"
+	---help---
+	  This driver provides support for Intel P-Unit Mailbox IPC mechanism,
+	  which is used to bridge the communications between kernel and P-Unit.
 endif # X86_PLATFORM_DEVICES