rex: Add "dynamic-speed" property
rex: Add "dynamic-speed" property

This patch enables `dynamic-speed` property for I2C4. For Rex
platform, PD (parade/ps8815) is attached to the I2C4.

BUG=b:248775521
TEST=Able to perform PD sync without any error
Update auxfw 0
CBFS: Found 'ps8815_a2.bin' @0x18df00 size 0xfc1 in mcache @0x75c2d49c
vb2_digest_init: 4033 bytes, hash algo 2, HW acceleration enabled
ps8815.1: found SPI flash ID 0xef11
ps8815.1: updating base FW
ps8815.1: erased 4KB in 128ms
ps8815.1: erased 64KB in 1712ms
ps8815.1: verified 0KB in 6ms
ps8815.1: programming 64KB...
ps8815.1: programmed 64KB in 547ms (54867B skipped)
ps8815.1: verified 64KB in 3518ms
ps8815.1: reset MCU
ps8815.1: vendor 0x1da0 product 0x8815 device 0x0003 fw_rev 0x28

Signed-off-by: Subrata Banik <e712824c9e10f98cf0ef031b18b313746fdf839a@google.com>
Change-Id: I79c94083c60f2a97273c03d5c2569d3350e0eed4
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/3935738
Tested-by: Kapil Porwal <8dbae7bc8a18721b908ef4a9c1a11b4233643c33@chromium.org>
Commit-Queue: Subrata Banik <e712824c9e10f98cf0ef031b18b313746fdf839a@chromium.org>
Reviewed-by: Kapil Porwal <8dbae7bc8a18721b908ef4a9c1a11b4233643c33@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec