doc: uefi: Describe UEFI HTTPs boot

We now can use a combination og lwIP & mbedTLS and download from
https://. Describe the config options needed to enable it as well
as some limitations

Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Jerome Forissier <jerome.forissier@linaro.org>
Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
1 file changed