trivial: Style fix

pico_dev_eth: Bug fix

A simple linked-list bug: `buf_pool` has a free list for bookkeeping
free ethernet buffers, it keeps track of the index of the latest free
buffer (the head). Every time a new free buffer arrived, it updates
the head of the free list to the index of the new buffer, then stores
the index of the old head inside the new head's buffer. It wasn't
implemented properly as it stores the old head's index inside its own
buffer and does nothing to the new head's buffer.
This could cause random memory corruption bugs.

Fix: Store the index of the old head into the new free buffer correctly.

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'

libethdrivers: Fix indenting

libethdrivers: 64-bit compatibility fixes

Fix whitespace

- remove trailing whitespace
- remove duplicate blank lines
- remove blank lines at end of file

Fixed the Makefile to include pico_ethernet.c
Fixed libethdrivers/src/pico_dev_eth.c to compare the flag CONFIG_LIB_PICOTCP_ASYNC_DRIVER using #ifdef rather than if()
Fixed Kconfig description message

Create Kconfig options

Revert "Revert commits from picotcp"

This reverts commit ba4824bb8ca6fc42645d1dff9f323206177478f1.

Put in guards to prevent compilation issues when library is not in use.

Revert commits from picotcp

These commits introduce a dependency that has no clear resolution

Revert "Cleanup the code and update license"
This reverts commit 27104d0d4790489b6f2e46e2701d15f47fcc7f24.
Revert "Bug fix"
This reverts commit 6073c50b0aeb5d9e5e473275438393d1b1471264.
Revert "Add no malloc version of picotcp create"
This reverts commit 3d6d905ddf4040e2c873e4bd78bcd037d5b673c0.
Revert "Add picotcp to Kbuild"
This reverts commit 353a79b9c573dbc4e9b8c66abcb42a8128c66619.
Revert "Remove usage of deprecated LOG_ERROR function."
This reverts commit 1109941bd0cefe1764676c7b855636a2e6bf12f7.
Revert "Add a shared buffer for rx and tx."
This reverts commit 1a879aa7c77a600c2b13a5d03fd4d87f2fe896b9.
Revert "Async driver interface for picotcp"
This reverts commit b5b81e9220bc2925e29b27cfb16080028f80fa7c.

Cleanup the code and update license

Bug fix

Add no malloc version of picotcp create

Remove usage of deprecated LOG_ERROR function.

Add a shared buffer for rx and tx.

Async driver interface for picotcp

Add an interface for PicoTCP