target: Minimize #include directives

Remove superfluous #include directives from the include/target/*.h
files. Add missing #include directives to other *.h and *.c files.
Use forward declarations for structures where possible. This
change reduces the build time for make M=drivers/target on my
laptop from 27.1s to 18.7s or by about 30%.

Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Bryant G. Ly <bryantly@linux.vnet.ibm.com>
diff --git a/drivers/target/iscsi/iscsi_target_erl1.h b/drivers/target/iscsi/iscsi_target_erl1.h
index 2a3ebf1..54d36bd 100644
--- a/drivers/target/iscsi/iscsi_target_erl1.h
+++ b/drivers/target/iscsi/iscsi_target_erl1.h
@@ -1,6 +1,16 @@
 #ifndef ISCSI_TARGET_ERL1_H
 #define ISCSI_TARGET_ERL1_H
 
+#include <linux/types.h>
+#include <scsi/iscsi_proto.h> /* itt_t */
+
+struct iscsi_cmd;
+struct iscsi_conn;
+struct iscsi_datain_req;
+struct iscsi_ooo_cmdsn;
+struct iscsi_pdu;
+struct iscsi_session;
+
 extern int iscsit_dump_data_payload(struct iscsi_conn *, u32, int);
 extern int iscsit_create_recovery_datain_values_datasequenceinorder_yes(
 			struct iscsi_cmd *, struct iscsi_datain_req *);