sysemu: Remove the ERBIUM_HIGH_MEMORY flag.

[glguida]

The addition at the last moment of this flag to mask a weird behaviour of the elf loader that is essenitally benign to the erbium implementation (as this seems some issue due to the linker scripts) is unnecessary.

The real approach here is to investigate why this was added, and find a better way to deal with it.

[vidas]

Thanks for the issue!

The goal of EMU_HAS_HIGH_MEMORY wasn't the high memory at all - I wanted to remove dram_base from a public interface of Erbium MainMemory (this is the only place where dram_base is referenced).

That this is benign to Erbium is not obvious immediately. And yes, it's a linker thing - ET-SoC-1 has DRAM mirrored at two ("low" and "high") addresses with different PMA properties. We don't know if there are elfs (DV tests?) in the wild that try to load into high memory, this change (b3b0534) suggest that there are.

EMU_HAS_HIGH_MEMORY is a way to say "this is ET-SoC-1 only" in machine readable way instead of leaving a comment in the code that there is no danger to Erbium.

I personally suggest to handle this in the memory map itself instead of a hack with assumptions and magical constants in the loader.

[glguida]

It is benign in erbium because we'll never use addresses this high. we're bound to 32 bit. If we decide to load an ELF that maps on top of that, it's okay to have a misbehaviour, until this is fixed.

I'd rather fix it properly than adding weird flags.