doc: cmake and minor documentation corrections

As using Make is deprecated,update the documentation
accordingly so that only the CMake build system,
commands and dependencies are mentioned.
This commit also updates some minor changes/errors
in documentation.

Signed-off-by: Tomás Agustín González Orlando <tomasagustin.gonzalezorlando@arm.com>
Change-Id: I563d9ee343b4ab07c4e0d8d4845b8b574b31dde0