recipes-bsp/u-boot: conditionally set can clock frequency based on SOM rev.

[vegano1]

Overview

The CAN clock frequency has changed from 20MHz to 40MHz as of Verdin iMX8M Mini Rev E, and since we have ordered a new batch of SOMs that will most likely be Rev E we need to support this change both at the factory to produce new robots but also for already deployed robots. This pull request updates the u-boot script to conditionally apply the "verdin-imx8mm_MCP2518_overlay.dtbo" overlay based on the SOM rev.

Closes: PLAT-464

Test Plan and Hands on Testing

• Flash a SOM and make sure the device boots up
• Flash a rev E SOM and make sure the can clock is set to 40Mhz.
• Flash a rev D or lower SOM and make sure the can clock is set to 20Mhz.
• Perform an OTA update on a rev E SOM and make sure the system boots and can clock stays at 40Mhz
• Perform an OTA update on a < rev E SOM and make sure the system boots and CAN clock stays at 20Mhz
• Make sure that the SOM can communicate with all CAN subsystems on the Flex (head, axis, gripper, etc)

Changelog

• Conditionally apply the "verdin-imx8mm_MCP2518_overlay.dtbo" overlay for SOM revs lower than E.

Risk assessment

High, while this won't affect devices on the field, it will affect new SOMs flashed, so we need to ensure adequate testing.

[sfoster1]

I think there's an issue in the skip logic that we can fix and improve the readability at the same time

[sfoster1]

Awesome, looks great to me!