replace kernel_autoconf with sel4_autoconf

since the mainline kernel's kernel_autoconf doesn't include
seL4/gen_config.h but sel4_autoconf does

libethdrivers: include config of lwip and picotcp

since global autoconf is removed, we need to explicitly
include the config of lwip and picotcp which will further
indicate the existance of corresponding lib

util_libs: remove autoconf.h from util_libs

this commit removes autoconf.h generation from each lib and
append '#include <<lib_name>/gen_config.h>' after each
'#include <autoconf.h>' since autoconf.h is only the for the
kernel config now. This is a temporarily solution, since we
currently don't have a way to tell which header files each file
is trying to include when it includes 'autoconf.h'

libfdt: Added libfdt library

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

picotcp: Port to CMake

liblwip: CMakeLists adds liblwip subdirectory

Updated root CMakeLists file to add liblwip subdirectory.

libethdrivers: cmake build definitions

libpci: cmake build definitions

Add CMake build rules for various libraries