ic2/designware: Move Intel i2c logic to shared driver

BUG=b:70232394
BRANCH=none
TEST=emerge-reef coreboot
emerge-glados

Change-Id: Idb453a4d2411163e6b4a8422310bf272eac5d379
Signed-off-by: Chris Ching <chingcodes@chromium.org>
Reviewed-on: https://review.coreboot.org/22822
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/soc/intel/skylake/Kconfig

@@ -334,6 +334,10 @@ config SOC_INTEL_COMMON_LPSS_CLOCK_MHZ
 	int
 	default 120
 
+config DRIVERS_I2C_DESIGNWARE_CLOCK_MHZ
+	int
+	default SOC_INTEL_COMMON_LPSS_CLOCK_MHZ
+
 config SOC_INTEL_COMMON_BLOCK_GSPI_MAX
 	int
 	default 2