archiver.bbclass: Add ENABLE_COPYLEFT_FILTER to enable/disable copyleft_filter.bbclass

archiver.bbclass: Add ENABLE_COPYLEFT_FILTER to enable/disable copyleft_filter.bbclass

Set it to 0 can make it archive all the used sources during the build, nothing
will be filtered out, this is useful when we want to archive all the sources.

This equals to:
COPYLEFT_LICENSE_INCLUDE = "*"
COPYLEFT_LICENSE_EXCLUDE = ""

But there are a lot of settings in copyleft_filter.bbclass, so it may not work
when its default settings are changed, add the var ENABLE_COPYLEFT_FILTER will
make it more reliable.

The default value is 1, has no impact by default.

Signed-off-by: Robert Yang <liezhi.yang@windriver.com>