MLBEDSW-3509: Updated the debug database to support multiple custom operators.

Previously the debug database lost some operators in the debug database outputs when multiple custom operators were generated by Vela.
Also, the file offsets for command streams were always 0, even for a single custom operator. This patch should rectify these problems.

Signed-off-by: erik.andersson@arm.com <erik.andersson@arm.com>
Change-Id: Ieb072440d4f1806d4833a676683b4f42f431f3df