mb/google/rex/var/rex0: Configure I2C5 timing

Configure I2C5 timing in devicetree to ensure I2C devices
meet timing requirement.

BUG=b:300177424
TEST=Build and check I2C devices timing meet spec.

|             | I2C5-Before | I2C5-After |
|-------------|-------------|------------|
| FSMB(KHz)   | 445.400     |   343.638  |
| TLOW(us)    | 1.543       |   2.068    |
| THIGH(us)   | 0.475       |   0.604    |
| THD:STA(us) | 0.603       |   0.711    |
| TSU:STA(us) | 0.612       |   0.611    |
| TSU:STO(us) | 0.605       |   0.611    |
| TBUF(us)    | >1.914      |   >2.044   |

Change-Id: I3bb678b66d55c6bfaff76e3e5500a2a3bc3a2c61
Signed-off-by: Ivy Jian <ivy.jian@quanta.corp-partner.google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/78111
Reviewed-by: Subrata Banik <subratabanik@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/src/mainboard/google/rex/variants/rex0/overridetree.cb b/src/mainboard/google/rex/variants/rex0/overridetree.cb
index d92dc24..1d4ba63 100644
--- a/src/mainboard/google/rex/variants/rex0/overridetree.cb
+++ b/src/mainboard/google/rex/variants/rex0/overridetree.cb
@@ -142,8 +142,8 @@
 		},
 		.i2c[5] = {
 			.speed = I2C_SPEED_FAST,
-			.rise_time_ns = 900,
-			.fall_time_ns = 400,
+			.rise_time_ns = 400,
+			.fall_time_ns = 280,
 			.data_hold_time_ns = 50,
 		},
 	}"