mm/memblock: export memblock_{start/end}_of_DRAM

[Christoph Hellwig]

On Fri, Oct 30, 2020 at 10:38:42AM +0200, Mike Rapoport wrote:
>  
> What do you mean by "system memory block"? There could be a lot of
> interpretations if you take into account memory hotplug, "mem=" option,
> reserved and firmware memory.
> 
> I'd suggest you to describe the entire use case in more detail. Having
> the complete picture would help finding a proper solution.

I think we need the code for the driver trying to do this as an RFC
submission.  Everything else is rather pointless.