dfu: Export allocated dfu buffer size

The method for exporting size of allocated buffer is provided.
It is afterwards used by USB's dfu function code.

Signed-off-by: Lukasz Majewski <l.majewski@samsung.com>

drivers/dfu/dfu.c

@@ -74,6 +74,11 @@ unsigned char *dfu_free_buf(void)
 	return dfu_buf;
 }
 
+unsigned long dfu_get_buf_size(void)
+{
+	return dfu_buf_size;
+}
+
 unsigned char *dfu_get_buf(void)
 {
 	char *s;

include/dfu.h

@@ -131,6 +131,7 @@ bool dfu_reset(void);
 int dfu_init_env_entities(char *interface, int dev);
 unsigned char *dfu_get_buf(void);
 unsigned char *dfu_free_buf(void);
+unsigned long dfu_get_buf_size(void);
 
 int dfu_read(struct dfu_entity *de, void *buf, int size, int blk_seq_num);
 int dfu_write(struct dfu_entity *de, void *buf, int size, int blk_seq_num);