mainboard/google/octopus/variants/casta: Decrease touchpad I2C CLK frequency

ELAN touchpad supports up to 400KHz, so we need to limit its CLK
frequency to 400HKz.

BUG=b:123376618
BRANCH=octopus
TEST=built and verified touchpad I2C clk frequency gets be lower than 400KHz

Change-Id: If7a43fe20c7e5abdf23c8c36e34c072c371563bf
Signed-off-by: Seunghwan Kim <sh_.kim@samsung.com>
Reviewed-on: https://review.coreboot.org/c/31085
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Furquan Shaikh <furquan@google.com>

src/mainboard/google/octopus/variants/casta/overridetree.cb

@@ -1,5 +1,4 @@
 chip soc/intel/apollolake
-
 	# Intel Common SoC Config
 	#+-------------------+---------------------------+
 	#| Field             |  Value                    |
@@ -8,12 +7,20 @@ chip soc/intel/apollolake
 	#|                   | required to set up a BAR  |
 	#|                   | for TPM communication     |
 	#|                   | before memory is up       |
+	#| I2C5              | Audio                     |
+	#| I2C6              | Trackpad                  |
 	#+-------------------+---------------------------+
 	register "common_soc_config" = "{
 		.gspi[0] = {
 			.speed_mhz = 1,
 			.early_init = 1,
 		},
+		.i2c[6] = {
+			.speed = I2C_SPEED_FAST,
+			.rise_time_ns = 66,
+			.fall_time_ns = 90,
+			.data_hold_time_ns = 350,
+		},
 	}"
 
 	device domain 0 on