testsuite: add tests for weak dependencies

testsuite: add tests for weak dependencies

The following tests to verify weak dependencies have been implemented:
1) modprobe test to check that related weakdep modules are not loaded
   due to being a weakdep.
2) depmod test to check weakdep output.
3) user test to check that configuration files with weakdep are parsed
   correctly and related weakdep modules can be read correctly from user
   applications.

Signed-off-by: Jose Ignacio Tornos Martinez <jtornosm@redhat.com>
Link: https://lore.kernel.org/r/20240530070836.9438-1-jtornosm@redhat.com
[ Minor whitespace issues and define MODULE_WEAKDEP if it's not defined
  already ]
Signed-off-by: Lucas De Marchi <lucas.de.marchi@gmail.com>