[FEATURE] Implement Kernel build for RPi 4B SMP

[linguini1]

Is your feature request related to a problem? Please describe.

The RPi 4B support currently uses a bundled image where there is only one memory region shared by the user and the kernel.

Describe the solution you'd like

NuttX supports userspace/kernel space separation with kernel mode builds. I would like a kernel mode build to be supported for the Pi 4B with a correct linker script, configuration defconfig preset and some loaded tests to verify correct operation.

Describe alternatives you've considered

No response

Verification

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