u-boot: Detect CPU revision

[openedev]

Reference:

https://github.com/radxa/kernel/blob/linux-5.10-gen-rkr4.1/drivers/cpufreq/rockchip-cpufreq.c#L231

1. Find the CPU version
2. Print the found CPU
   sample log

CPU:   Rockchip RK3588J rev1.2 at 792MHz
CPU:   Industrial temperature grade (-40C to +85C) at 28C

3. Enable SPL multi DTB for Neu6a, Neu6b
4. Load the right dtb based on the found CPU

Support this in Mainline as well BSP U-boot.