Build: Convert platform dir to modern cmake

Rewrite cmake files inside the platform directory. Removed generated
files as they are now generated into the build tree. Move Mbed Crypto
config files to lib/ext/mbedcrypto. Alter 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: I54c6ec5e0256032450260a1b0ac9702bc8ca3700
Signed-off-by: Raef Coles <raef.coles@arm.com>
21 files changed