image: Expand kernel buffer size to 512MB
This patch expands the kernel buffer to 512MB (or to 128MB on arm32 devices where that's the Linux ABI limit anyway, or to less on some older specialty platforms where it otherwise wouldn't fit). The kernel partition size on disk has traditionally only been 16MB, and we don't plan on changing that... however, on a recovery USB stick we can make the partition as large as we want, and we may need to do that if we want to add more stuff to the recovery initramfs. Unfortunately we'll be stuck with the exisiting limits on old platforms since recovery firmware is not updateable, but this CL is meant to ensure that we'll at least have lots of headroom to grow on future platforms.
Some memory layouts had to be adjusted to fit the new buffer. Also document the individual arch-dependent constraints for placing various regions in the Kconfig help (some of these only apply to older Linux versions, but since we don't update our kernels it's better to mention everything that might apply... boards can still violate them after they made sure that they're unaffected).
BRANCH=None BUG=chromium:873135 TEST=Booted Cheza (not feasible to test every platform, I've double-checked everything manually as best as I could).
Change-Id: I23f1a2c78f4e82c1f1e4a16d823ab36d2e90ef1d Signed-off-by: Julius Werner firstname.lastname@example.org Reviewed-on: https://chromium-review.googlesource.com/1179122 Reviewed-by: Aaron Durbin email@example.com