mb/google/sarien: Set initial I2C bus rise/fall times

Provide rise/fall times as measured on existing boards.  This will
need adjusted for new boards but provides a starting point that
makes I2C clocks look reasonable.

Tested by measuring I2C bus speed and rise/fall times with a scope.

Change-Id: Ic18010f5efc41dcee8925d696767ba2c44e3df4b
Signed-off-by: Duncan Laurie <dlaurie@google.com>
Reviewed-on: https://review.coreboot.org/c/30069
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-by: Lijian Zhao <lijian.zhao@intel.com>

src/mainboard/google/sarien/variants/arcada/devicetree.cb

@@ -67,10 +67,14 @@ chip soc/intel/cannonlake
 		},
 		.i2c[1] = {
 			.speed = I2C_SPEED_FAST,
+			.rise_time_ns = 216,
+			.fall_time_ns = 28,
 		},
 		.i2c[4] = {
 			.early_init = 1,
 			.speed = I2C_SPEED_FAST,
+			.rise_time_ns = 452,
+			.fall_time_ns = 110,
 		},
 	}"
 

src/mainboard/google/sarien/variants/sarien/devicetree.cb

@@ -67,10 +67,14 @@ chip soc/intel/cannonlake
 		},
 		.i2c[1] = {
 			.speed = I2C_SPEED_FAST,
+			.rise_time_ns = 290,
+			.fall_time_ns = 110,
 		},
 		.i2c[4] = {
 			.early_init = 1,
 			.speed = I2C_SPEED_FAST,
+			.rise_time_ns = 280,
+			.fall_time_ns = 90,
 		},
 	}"