x86: add support for Intel Low Power Subsystem

We are starting to see traditional SoC peripherals also in the x86 world in
chips like Intel Lynxpoint. Typically we already have a Linux driver for
the peripheral but it takes advantage of the common clk framework to
control and retrieve information about the peripheral clock.

So far there hasn't been a standard way on x86 to pass information such as
clock rate from whatever the configuration system is used to the driver,
but instead different variations have emerged, like adding this information
to the platform data.

Solve this by adding a new config option X86_INTEL_LPSS. If this is
selected we enable common clk framework (and everything else) that is
needed to support the Intel LPSS drivers.

Enabling common clk framework on x86 was originally proposed by Mark Brown.

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>