UBUNTU: kbuild: generate modules.builtin

To make it easier for module-init-tools and scripts like mkinitrd to
distinguish builtin and missing modules, install a modules.builtin file
listing all builtin modules. This is done by generating an additional
config file (tristate.conf) with tristate options set to uppercase 'Y'
or 'M'. If we source that config file, the builtin modules appear in
obj-Y.

Conflicts:

	Makefile

Signed-off-by: Michal Marek <mmarek@suse.cz>
Signed-off-by: Andy Whitcroft <apw@canonical.com>

(cherry picked from commit 32da55f0

)
Signed-off-by: Bryan Wu <bryan.wu@canonical.com>
Signed-off-by: Andy Whitcroft <apw@canonical.com>