fpga: manager: add owner module and take its refcount

In the Linux kernel, the following vulnerability has been resolved:

fpga: manager: add owner module and take its refcount

The current implementation of the fpga manager assumes that the low-level

module registers a driver for the parent device and uses its owner pointer

to take the module's refcount. This approach is problematic since it can

lead to a null pointer dereference while attempting to get the manager if

the parent device does not have a driver.

To address this problem, add a module owner pointer to the fpga_manager

struct and use it to take the module's refcount. Modify the functions for

registering the manager to take an additional owner module parameter and

rename them to avoid conflicts. Use the old function names for helper

macros that automatically set the module that registers the manager as the

owner. This ensures compatibility with existing low-level control modules

and reduces the chances of registering a manager without setting the owner.

Also, update the documentation to keep it consistent with the new interface

for registering an fpga manager.

Other changes: opportunistically move put_device() from __fpga_mgr_get() to

fpga_mgr_get() and of_fpga_mgr_get() to improve code clarity since the

manager device is taken in these functions.