fpga: add altera freeze bridge support

Add a low level driver for Altera Freeze Bridges to the FPGA Bridge
framework.  A freeze bridge is a bridge that exists in the FPGA
fabric to isolate one region of the FPGA from the busses while that
one region is being reprogrammed.

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