Add support for MikroTik RB5009UG

@adron Here is the SPI-NOR dump:
https://drive.google.com/drive/folders/1WnswllcXaAgT8hKBx4Imzr_FRHWunpL4?usp=sharing

I have also traced most of the pins on the SPI+UART header.

1   GND Vcc  RX  ?  GND
   #--------------------#
   |.-. .-. .-. .-. .-. |
   |'-' '-' '-' '-' '-' |
   |.-. .-. .-. .-. .-. |
   |'-' '-' '-' '-' '-' |
   #--------------------#
2   CLK  DO /CS  TX  DI

Those pads marked RX and TX are meant for the unpopulated PoE MCU it seems as they end on its pads.

I can see:

BootROM - 2.03
Starting AP IOROM 1.02
Booting from SPI NOR flash 0
Found valid image at boot postion 0x000
lmv_ddr: mv_ddr-1.1.0-g8c6defd127 (Aug 03 2021 - 18:17:37)
mv_ddr: completed successfully
BL2: Initiating SCP_BL2 transfer to SCP

So UART needs to be enabled in the hard config as it's disabled in ATF and later.
I have changed:
15 00 04 00 05
to
15 00 04 00 00

But UART still stops working