Convert the generic fpga region DT binding to json-schema.
There are some differences compare to txt version.
1. DT overlay can't be described in example that's why directly include
information from overlay to node which was referenced. It is visible in
example with /* DT Overlay contains: &... */

2. All example have been rewritten to be simpler and describe only full
reconfiguration and partial reconfiguration with one bridge.
Completely drop the case where fpga region can inside partial
reconfiguration region which is already described in description

3. Fixed some typos in descriptions compare to txt version but most of it
is just c&p from txt file.
Signed-off-by: Michal Simek <michal.simek@amd.com>
Link: https://lore.kernel.org/r/37b107d86b39ef4bc9c482b57b27de8b92c3fa43.1706530726.git.michal.simek@amd.comSigned-off-by: Rob Herring <robh@kernel.org>