DES and DOCSIS DES cipher implementation added

Notes:
- DOCSIS DES is based on DES cipher implementation
- Current DES implementation is very basic: functional but inefficient.
  It is implemented in plain C and very close to original FIPS46-3 specification.
  It will be optimized in the future and some architecture specific versions may also appear.

Change-Id: Iff38fe724387d2b3073ce12ee218bdc14969379f