powerpc: Repair device bindings documentation

Commit d0fc2eaa "powerpc/fsl: Refactor
device bindings" split out a number of device bindings from
booting-without-of.txt into separate files.  Having them all in one file
was a frequent source of merge conflicts.

However, in the next merge, 49997d75, there
was another conflict.  Some of the bindings removed from
booting-without-of.txt were mistakenly added back in and the copies in
dts-bindings were kept as well.

This patch re-removes "Freescale Display Interface" and "Freescale on board
FPGA" and fixes the table of contents.

Signed-off-by: Trent Piepho <tpiepho@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>