fpga: clean up fpga Kconfig

The fpga menuconfig has gotten messy.  The bridges and managers are
mixed together.

* Separate the bridges and things dependent on CONFIG_FPGA_BRIDGE
  from the managers.
* Group the managers by vendor in order that they were added
  to the kernel.

The following is what the menuconfig ends up looking like more or less
(platform dependencies are hiding some of these on any given
platform).

    --- FPGA Configuration Framework
    <*>   Altera SOCFPGA FPGA Manager
    <*>   Altera SoCFPGA Arria10
    <*>   Altera Partial Reconfiguration IP Core
    <*>     Platform support of Altera Partial Reconfiguration IP Core
    <*>   Altera FPGA Passive Serial over SPI
    <*>   Altera Arria-V/Cyclone-V/Stratix-V CvP FPGA Manager
    <*>   Xilinx Zynq FPGA
    <*>   Xilinx Configuration over Slave Serial (SPI)
    <*>   Lattice iCE40 SPI
    <*>   Technologic Systems TS-73xx SBC FPGA Manager
    <*>   FPGA Bridge Framework
    <*>     Altera SoCFPGA FPGA Bridges
    <*>     Altera FPGA Freeze Bridge
    <*>     Xilinx LogiCORE PR Decoupler
    <*>     FPGA Region
    <*>       FPGA Region Device Tree Overlay Support

Signed-off-by: Alan Tull <atull@kernel.org>
Acked-by: Moritz Fischer <mdf@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>