spdx: add option to include only compiled sources

spdx: add option to include only compiled sources

When SPDX_INCLUDE_COMPILED_SOURCES is enabled, only include the
source code files that are used during compilation.

It uses debugsource information generated during do_package.

This enables an external tool to use the SPDX information to disregard
vulnerabilities that are not compiled.

As example, when used with the default config with linux-yocto, the spdx size is
reduced from 156MB to 61MB.

Tested with bitbake world on oe-core.

CC: Quentin Schulz <quentin.schulz@cherry.de>
CC: Joshua Watt <JPEWhacker@gmail.com>
CC: Peter Marko <peter.marko@siemens.com>
Signed-off-by: Daniel Turull <daniel.turull@ericsson.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>