fpga: mgr: add devm_fpga_mgr_create

Add devm_fpga_mgr_create() which is the managed
version of fpga_mgr_create().

Change current FPGA manager drivers to use
devm_fpga_mgr_create()

Signed-off-by: Alan Tull <atull@kernel.org>
Suggested-by: Federico Vaga <federico.vaga@cern.ch>
Acked-by: Moritz Fischer <mdf@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>