liblwip: Exclude lwipopts.h

Including the library's version of lwipopts.h config prevents users from
using a custom version of the lwipopts.h config file for each
application and instead restricts the user to having to modify the
library's version of lwipopts.h which isn't a suitable workflow.

This commit excludes the library's version of lwipopts.h from the build.
Users are now required to use the CMake macro inside the
lwip_helpers.cmake file to include a custom version of lwipopts.h. Also
update style filter to point to the new default lwipopts.h location.

style: Add lwipopts.h to the style filter

This file should not be styled according to our style guide as it is
related to an external library.

trivial: Fix .stylefilter to not filter every file

libfdt: Added libfdt library

Added the libfdt library from linux kernel sourced from
linux kernel version : 5.0.6.