Embryo should use the memory atag.

[tornewuff]

The bootstrap assumes it's okay to allocate pages from the space after where the rom was loaded. The ARM linux boot protocol kinda guarantees that 16KB of ram is available below the beginning of the rom, which we use, but nothing else (and even this doesn't exist in xip). It should instead parse the ATAGs to find where physical ram is.

We also don't work in XIP configs or if loaded to a non-page-aligned address...