buildroot

packages: remove all := signs

Finally get rid of all := used for variable definitions in packages,
as we suggest in our manual and during the review of new packages.

While I was at it, I also sometimes added a few missing new lines
between the header and the first variable definition.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>