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>

include/linux/fpga/fpga-mgr.h

@@ -117,6 +117,8 @@ int fpga_mgr_firmware_load(struct fpga_manager *mgr, u32 flags,
 
 struct fpga_manager *of_fpga_mgr_get(struct device_node *node);
 
+struct fpga_manager *fpga_mgr_get(struct device *dev);
+
 void fpga_mgr_put(struct fpga_manager *mgr);
 
 int fpga_mgr_register(struct device *dev, const char *name,