spi: intel: Add support for second flash chip

Intel SPI flash controller has been supporting two chip selects long
time already even if the most common configuration is to have a single
flash chip for the BIOS and related data. This adds support for the
second chip select if we find out that there are two flash components
(this information is available in the mandatory flash descriptor on the
first chip). The second chip is exposed as is without any partition
information.

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Link: https://lore.kernel.org/r/20220816130818.89600-1-mika.westerberg@linux.intel.com
Signed-off-by: Mark Brown <broonie@kernel.org>