spi support for Exynos Auto v9 SoC

Merge series from Chanho Park <chanho61.park@samsung.com>:

Add to support Exynos Auto v9 SoC's spi. By supporting USI(Universal
Serial Interface) mode, the SoC can support up to 12 spi ports. Thus, we
need to increase MAX_SPI_PORTS from 6 to 12. The spi of the SoC can
support loopback mode unlike previous exynos SoCs. To separate the
feature, we need to add .has_loopback to the s3c64xx_spi_port_config.
Furthermore, it uses 4 as the default internal clock divider. We also
need to clk_div field of the structure and assign "2" as the default
value to the existing SoC's port config.
Device tree definitions of exynosautov9-spi will be added in separated
patchset to include usi(i2c/uart/spi) nodes all together.