UBUNTU: [Debian]: dkms-build: new parameter for debug package directory

UBUNTU: [Debian]: dkms-build: new parameter for debug package directory

BugLink: https://bugs.launchpad.net/bugs/1840704
Provide the 'dkms-build' script an argument that specifies
the path for installing modules built with debug symbols,
and update callers (currently just 'build_dkms' function)
and post-processor scripts for consistency (nvidia, vbox).

This is similar to the currently used package directory
argument 'pkgdir/lib/modules/abi-release/kernel', where
modules are installed anyway regardless of debug symbols.

The proposal is that the 'dkms-build' script, if provided
such argument, should handle the generation and stripping
of debug symbols, and installing the non-stripped modules
into the debug package directory and the stripped modules
into the other package directory (which is used currently).

The script double checks whether debug symbols are indeed
present in the module file (via the '.debug_info' section)
to avoid non-debug modules in the debug package directory,
with an additional benefit of backwards compatibility and
gracefully handling DKMS packages that do not yet support
building debug symbols (or that failed to for some reason).

The script should not handle the '.gnu_debuglink' section
to reference the non-stripped modules in stripped modules
(and re-signinig afterward), as this is now done in rules
after the DKMS modules have been built and installed.

This currently does nothing as no DKMS modules are built
with debug symbols (so this keeps the new argument empty).

This will allow for some of the DKMS-built modules to be
shipped with debug symbols to aid with debug and support.

Signed-off-by: Mauricio Faria de Oliveira <mfo@canonical.com>
Acked-by: Seth Forshee <seth.forshee@canonical.com>
Acked-by: Acked-by: Andy Whitcroft <apw@canonical.com>
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>