buildroot

core/apply-patches: store full path of applied patches

Currently, we only store the filename of the applied patches.

However, we are soon to want to install those patches in the legal-info
directory, so we'll have to know where those patches come from.

Instead of duplicating the logic to find the patches (bundled,
downloaded, from a global patch dir...), just store the full path to
each of those patches so we can retrieve them more easily later on.

Also always create the list-file, even if empty, so that we need not
test for its existence before reading it.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Luca Ceresoli <luca@lucaceresoli.net>
Reviewed-by: Luca Ceresoli <luca@lucaceresoli.net>
[Tested only with patches in the Buildroot sources]
Tested-by: Luca Ceresoli <luca@lucaceresoli.net>
Reviewed-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
[Thomas: used $PWD instead of $(pwd), as suggested by Arnout.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>