Replace string arrays with const char * and allocated space (part 1)

This commit deals with default_programmer, default_serial, default_parallel
and default_spi. The long term objective is to remove all fixed-size buffers
from the structures that lexer.l and config_gram.y deal with.

src/config.h

@@ -30,8 +30,6 @@
 #endif
 
 
-#define MAX_STR_CONST 1024
-
 enum { V_NONE, V_NUM, V_NUM_REAL, V_STR };
 typedef struct value_t {
   int      type;