[StarBook Mk VI - AMD] - Add option to set VRAM allocation

[Sean-StarLabs]

Discussed in #163

^{Originally posted by mrusme May 29, 2024}
I'd suggest un-hiding the setting for configuring minimum VRAM allocation in the AMI firmware, as the default 512MB seems to be making life hard sometimes. Since I see no reason for why users shouldn't be able to change VRAM allocation on their own, allowing this could make life a bit easier, especially when dealing with AMD ROCm, it seems.