Add kaslrseed to Rockchip's u-boot

[Manouchehri]

Description

Partly resolves #4306.

How Has This Been Tested?

If the kaslrseed command hasn't been compiled in to u-boot, it gracefully skips generating the kASLR

• Booted on a NanoPi R4S

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules

[Manouchehri]

For this to work, #4311 has to be merged in too.

[igorpecovnik]

OK, when you are done, label both with "Ready"

[Manouchehri]

Done, tested and KASLR is working for me.

[RlndVt]

If the kaslrseed command hasn't been compiled in to u-boot, it gracefully skips generating the kASLR

With gracefully skips, do you mean: "Unknown command ' kaslrseed ' - try 'help'"?

This message is concerning at first glance, can we add a check if we can find kaslrseed first?