With the Kendryte K210 platform code cleanup, none of the code copied
from Kendryte standalone SDK remains and this platform code is now
entirely licensed under OpenSBI BSD-2-clause license. Update the
README.md and ThirdPartyNotices.md files to reflect this.

Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Anup Patel <anup.patel@wdc.com>