event/opdl: fix license header and SPDX tags

event/opdl: fix license header and SPDX tags

This patch ensures that the OPDL files all contain correct SPDX tags.
The following changes were made to achieve this:
* replace license text with SPDX tag
* correct occurences where SPDX tag was not on first line of file
* ensure license years were correct

Fixes: 4236ce9bf5bf ("event/opdl: add OPDL ring infrastructure library")
Fixes: 3c7f3dcfb099 ("event/opdl: add PMD main body and helper function")
Fixes: d548ef513cd7 ("event/opdl: add unit tests")
Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
Acked-by: Liang Ma <liang.j.ma@intel.com>