UBUNTU: [Packaging] make firmware and modules available for ubuntu-core-initramfs

Signed-off-by: Wen-chien Jesse Sung <jesse.sung@canonical.com>
(backported from commit 24f0a5d7e6dbf2d1c6f18e0a4e27773c347aea69)
(source: https://git.launchpad.net/~canonical-kernel/denver/+git/linux-denver

)
Signed-off-by: Shrirang Bagul <shrirang.bagul@canonical.com>