coreboot_tables: Minor refactoring to reduce redundant data structures

There are three Coreboot table tags that all define some kind of memory
region, and each has their own homologous struct. I'm about to add a
fourth so I'll just clean this up and turn it into a generic struct
lb_range instead.

BUG=chrome-os-partner:21969
TEST=None

Change-Id: Id148b2737d442e0636d2c05e74efa1fdf844a0d3
Signed-off-by: Julius Werner <jwerner@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/167154
5 files changed