How to redirect GRUB2 output to a MMIO serial UART?

[Konstantin Aladyshev]

Is it possible to redirect GRUB2 output to a MMIO serial UART?

For example I have a UART that is displayed in a Linux boot log as:
```
AMDI0020:01: ttyS5 at MMIO 0xfedca000 (irq = 4, base_baud = 3000000) is a 16550A
```

To get kernel boot log, I just add this kernel parameter:
```
console=uart,mmio32,0xfedca000,115200n8
```

But how to redirect GRUB2 output to such kind of UART?

Best regards,
Konstantin Aladyshev