CGpt: Add 200MiB to the Rootfs

We have ongoing efforts to reduce the size of the rootfs but
will need buffer until those things happen.

I've also gone ahead and cleaned up redundant definition of the fs
size defined by layouts that should just inherit from base.

BUG=chromium:344725
TEST=cgpt debug and many grep searches through overlays to validate
this is the only file that needed changing.

Change-Id: I1424fc17c8b6a9de600eb1e97e05245937f5459c
Reviewed-on: https://chromium-review.googlesource.com/187034
Reviewed-by: Chris Sosa <sosa@chromium.org>
Tested-by: Chris Sosa <sosa@chromium.org>
Commit-Queue: Chris Sosa <sosa@chromium.org>
1 file changed