soc/intel/common/lpss_i2c: simplify API and use common config structure

The apollolake and skylake had duplicate stanzas of code for
initializing the i2c buses. Additionally, they also had very
similar structures for providing settings for the i2c speed
control. Introduce a new struct lpss_i2c_bus_config and
utilize it in both apollolake and skylake thereby removing
the need for SoC-specific structres. The new structure is
used for initializing a bus fully as the lpss i2c API is
simplified in that lpss_i2c_init() is only required to be
called. The struct lpss_i2c_bus_config structure is passed
in for both initializing and filling in the SSDT information.
The formerly exposed functions are made static to reduce the
external API exposure.

BUG=chrome-os-partner:58889

Change-Id: Ib4fa8a7a4de052da75c778a7658741a5a8e0e6b9
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: https://review.coreboot.org/17348
Reviewed-by: Furquan Shaikh <furquan@google.com>
Tested-by: build bot (Jenkins)
Reviewed-by: Duncan Laurie <dlaurie@chromium.org>

src/soc/intel/skylake/chip.h

@@ -201,7 +201,7 @@ struct soc_intel_skylake_config {
 	/* I2C */
 	/* Bus voltage level, default is 3.3V */
 	enum skylake_i2c_voltage i2c_voltage[SKYLAKE_I2C_DEV_MAX];
-	struct skylake_i2c_config i2c[SKYLAKE_I2C_DEV_MAX];
+	struct lpss_i2c_bus_config i2c[SKYLAKE_I2C_DEV_MAX];
 
 	/* Camera */
 	u8 Cio2Enable;