cve-check: add CVE_CHECK_REPORT_PATCHED variable to suppress reporting of patched CVEs

Default behavior is not changed. To suppress patched CVEs, set:

        CVE_CHECK_REPORT_PATCHED = ""

Signed-off-by: Chris Laplante <chris.laplante@agilent.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>