LICENSES: Add ISC license text

Add the full text of the ISC license to the kernel tree. It was copied
directly from:

   https://spdx.org/licenses/ISC.html



With the mention of "ISC" in the warranty disclaimer replaced with
"THE AUTHOR" as done in the ISC license headers used in the ath10k and
brcmfmac wifi drivers.

Cc: Kalle Valo <kvalo@codeaurora.org>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>