soc/intel/lpss: Provide common LPSS clock config

Since there are multiple controllers in the LPSS and all use the same
frequency, provide a single Kconfig option for LPSS_CLOCK_MHZ.

BUG=b:35583330

Change-Id: I3c0cb62d56916e6e5f671fb5f40210f4cb33316f
Signed-off-by: Furquan Shaikh <furquan@chromium.org>
Reviewed-on: https://review.coreboot.org/19115
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Tested-by: build bot (Jenkins)

src/soc/intel/apollolake/Kconfig

@@ -117,8 +117,7 @@ config CPU_ADDR_BITS
 	int
 	default 36
 
-config SOC_INTEL_COMMON_LPSS_I2C_CLOCK_MHZ
-	depends on SOC_INTEL_COMMON_LPSS_I2C
+config SOC_INTEL_COMMON_LPSS_CLOCK_MHZ
 	int
 	default 133