DTV: LDPC encoder: refactoring

* use uint16_t instead of int for tables
  * half the storage: should increase cache locality significantly
  * prefer unsigned types for unsigned jobs (here: indexing)
* convert humongous macro to template function
  * type safety
  * found and eliminated unused variables
  * cleaner code
  * better compiler warnings

NB: This class came without ANY tests.

Author: marcusmueller