Get rid of build warnings

Get rid of build warnings

[Issue#] SSDWSSP-397
[Bug] Several warnings was appearing during package build
[Cause] These warnings mainly concern implicit functions declarations
and comparisons between variables of different types
[Solution] Adding function declarations, header file inclusions,
explicit cast operators.
Also 'Werror' flag is added to CMakeLists.txt .

[Verification] Successful compilation & all security tests successfully
completed on target device

Change-Id: I2387b829835319354097384497abd9f1eaec9636