fpga: add method to get fpga manager from device

The intent is to provide a non-DT method of getting
ahold of a FPGA manager to do some FPGA programming.

This patch refactors of_fpga_mgr_get() to reuse most of it
while adding a new method fpga_mgr_get() for getting a
pointer to a fpga manager struct, given the device.

Signed-off-by: Alan Tull <atull@opensource.altera.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/fpga/fpga-mgr.txt

@@ -38,11 +38,13 @@ To get/put a reference to a FPGA manager:
 -----------------------------------------
 
 	struct fpga_manager *of_fpga_mgr_get(struct device_node *node);
+	struct fpga_manager *fpga_mgr_get(struct device *dev);
+
+Given a DT node or device, get an exclusive reference to a FPGA manager.
 
 	void fpga_mgr_put(struct fpga_manager *mgr);
 
-Given a DT node, get an exclusive reference to a FPGA manager or release
-the reference.
+Release the reference.
 
 
 To register or unregister the low level FPGA-specific driver: