MLECO-2489: Minor addition for PlatformMath

Adding sine function and allowing FFTs to be computed for cases where
the FFT len is not a power of 2. In this case, the naive implementation
is used. Option for computing FFT for a complex vector has also been
added, although, the CMSIS-DSP flow needs to be tested.

Change-Id: Iad9902b946f3088de91a5f67acfb4cb3d0b00457