board: Add configuration for atria

Starting the atria project with dpi that fits the flash layout as well
as UX requirement. Also some FW UI assets are carved out into RW, to
save some space in RO section.

BUG=b:499426826
BRANCH=None
TEST=emerge-atria chromeos-bmpblk coreboot chromeos-bootimage

Change-Id: I17cbb952d3bc59b62f672d213133b54aff39ef57
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/bmpblk/+/7790300
Reviewed-by: Subrata Banik <subratabanik@chromium.org>
Commit-Queue: Karthik Ramasubramanian <kramasub@google.com>
Reviewed-by: Jon Murphy <jpmurphy@google.com>
Tested-by: Karthik Ramasubramanian <kramasub@google.com>
GitOrigin-RevId: 09be8d5c330f80f15cd0d02a2e3caf643232a794