mfd: intel_soc_pmic: Fix a mess with compilation units

Crystal Cove and Whiskey Cove are two different PMICs which are
installed on Intel Atom SoC based platforms.

Moreover there are two independent drivers that by some reason were
supposed (*) to get into one kernel module.

Fix the mess by clarifying Kconfig option for Crystal Cove and split
Whiskey Cove out of it.

(*) It looks like the configuration was never tested with
    INTEL_SOC_PMIC=n. The line in Makefile is actually wrong.

Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net> (supporter:ACPI)
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Zhang Rui <rui.zhang@intel.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>