Docs: Deprecate 'build_docs' folder

With the prefix 'build', user may delete 'build_docs' accidentally.
Deprecate 'build_docs' folder and move the only files 'conf.py' to
'docs' folder.

Change-Id: I701e279861afdc9b0f6cfd10b343643acd77e51d
Signed-off-by: Shawn Shan <Shawn.Shan@arm.com>
3 files changed