util/stream: Update OSTREAM_DEF

OSTREAM_DEF macro is utility macro for creating function table
for output stream with function names derived from stream type
name.

i.e. OSTREAM_DEF(mem) would create function table like this:
const struct out_stream_vft mem_vft = {
   .write = mem_write,
   .flush = mem_flush,
   .pump_from = mem_pump_from,
}
along with prototypes:
static int mem_write(struct out_stream *, const uint8_t *, uint32_t);
static int mem_flush(struct out_stream *);
static int mem_pump_from(struct out_stream *, struct in_stream *, uint32_t);

last function was late addition and is optional

This change removes requirement to define pump_from function from OSTREAM_DEF
User still can create function table with pump_from funtion without
using macro if pumping is required.

util/stream/include/stream/stream.h

@@ -127,11 +127,10 @@ struct mem_in_stream {
 #define OSTREAM_DEF(type) \
  static int type ## _write(struct out_stream *ostream, const uint8_t *buf, uint32_t count); \
  static int type ## _flush(struct out_stream *ostream); \
- static int type ## _pump_from(struct out_stream *ostream, struct in_stream *istream, uint32_t count); \
  const struct out_stream_vft type ## _vft = { \
  .write = type ## _write, \
  .flush = type ## _flush, \
- .pump_from = type ## _pump_from, \
+ .pump_from = NULL, \
  }
 
 #define OSTREAM_VFT(type, _write, _flush, _pump) \