Build: Convert interface dir to modern cmake

Rewrite cmake files inside the interface directory. Remove generated
files as they are now generated into the build tree. Modify header
includes where include paths have changed.

WARNING: This change will not build in isolation, it requires _all_
other cmake changes to successfully build. It is split out only for
clarity of changes.

Change-Id: I9ebfb1e31bebcba4a45ea3bb9ed0aa1c3d1c144d
Signed-off-by: Raef Coles <raef.coles@arm.com>
5 files changed