disk_layout: Introduce modern disk layout template

At this point, everybody is inheriting from legacy_disk_layout.json,
and then creating board-specific overlays that bump up the kernel
partition and rootfs partition sizes. The legacy_disk_layout.json
file cannot really be changed, as changing partition layouts for
shipping boards will likely break updates.

Introduce a new scheme where the common templates can be updated
without affecting new boards. The expectation is that the common
templates should evolve slowly, given how long legacy_disk_layout.json
has survived.

The v2 edition of the disk_layout file is a copy of
legacy_disk_layout.json, but with kernel partitions bumped up to 32MB,
EFI partitions bumped up to 64MB (since they hold 2 copies of the
kernel), and rootfs partitions bumped up to 4GB. It also removes some of
the obscure old padding, which was likely there to accommodate disk drive
peculiarities that no longer exist.

TEST=build_image --board=hatch (and kukui, cheza, kalista), and verify large partitions are aligned.

Change-Id: Ie0f4ebfeafac03372758a1fb4480a651a93ec58e
Reviewed-on: https://chromium-review.googlesource.com/1538304
Commit-Ready: Evan Green <evgreen@chromium.org>
Tested-by: Evan Green <evgreen@chromium.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
2 files changed