Banana Pi M5 memory detection issue

I have Manjaro running on a Banana Pi M5, but it is only detecting 1GB of the total 4GB memory.

```
[    0.000000] Memory: 895376K/1055748K available (15872K kernel code, 2242K rwdata, 6476K rodata, 3584K init, 675K 
bss, 94836K reserved, 65536K cma-reserved)
```

uBoot is detecting all the memory fine:

```
U-Boot 2015.01 (May 20 2021 - 12:59:31)

DRAM:  3.8 GiB
```

