Add pre and post configuration callbacks for Spartan FPGAs

This patch adds a post configuration callback for Spartan2/3 FPGAs.
pre and post configuration callback are now optional and
not called when the function pointer is set to NULL.

Signed-off-by: Matthias Fuchs <matthias.fuchs@esd-electronics.com>

include/spartan2.h

@@ -58,6 +58,7 @@ typedef struct {
 	Xilinx_init_fn	init;
 	Xilinx_done_fn	done;
 	Xilinx_wr_fn	wr;
+	Xilinx_post_fn	post;
 	int           	relocated;
 } Xilinx_Spartan2_Slave_Serial_fns;