classes/create-spdx: Fix up license reporting

Licenses reported in the SPDX documents should be either:
 A) A valid SPDX identifier cross referenced from the SPDX license
    database
 B) A "LicenseRef" to a license described in the SPDX document

The licensing code will now add a placeholder extracted license with
corresponding "LicenseRef" for any licenses that are not matched to the
SPDX database

Parenthesis in the license expression are now handled correctly

Signed-off-by: Joshua Watt <JPEWhacker@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>