mfd: lpc_ich: Add support for Intel Apollo Lake SoC

Intel Apollo Lake SoC exposes serial SPI flash through the LPC device. The
SPI flash host controller is not discoverable through PCI config cycles
because P2SB (function 0 of the device 13) is hidden by the BIOS. We unhide
the device briefly in order to read BAR 0 of the SPI host controller.

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Acked-by: Lee Jones <lee.jones@linaro.org>
Acked-by: Marek Vasut <marek.vasut@gmail.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>