net: share fastboot boot handle logic between transports

Introduce reboot, boot and continue commands support to
TCP fastboot by moving existing UDP logic into the common module.

Signed-off-by: Dmitrii Merkurev <dimorinny@google.com>
Cc: Ying-Chun Liu (PaulLiu) <paul.liu@linaro.org>
Cc: Simon Glass <sjg@chromium.org>
Сс: Joe Hershberger <joe.hershberger@ni.com>
Сс: Ramon Fried <rfried.dev@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Ramon Fried <rfried.dev@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>