cmake: Set C standard to 11 and CXX to 14

As we enabled project_options, we require to set these standards.
The numbers follow what we set in storage project and have used in
other projects as well.

This fixes the warnings:

```
-- The default CMAKE_CXX_STANDARD used by external targets and tools
is not set yet. Using the latest supported C++ standard that is 20
-- The default CMAKE_C_STANDARD used by external targets and tools is
not set yet. Using the latest supported C standard that is 17
```

Signed-off-by: Martin Kojtal <martin.kojtal@arm.com>