Detach disassembler

Detach disassembler from debugger.

* From now the only public interface to the disassembler
 should be the dt_trans function:

int dt_trans(int addr, char *buf, int dasm_mode);

* Disassembler clients should now be compiled with -DHAVE_DASM.
 CMake function "uses(file.c DASM)" can be used to facilitate
 this.

* Disassembler files have been moved to {include|src}/dasm
 directory.

* WITH_DASM cmake directive controls whether disassembler
 should be included.

* "cycle_ic" is an unconditional global CPU variable now.