compat-drivers: skip already appplied patches

GNU Patch does not yet support giving a different
error return value for patches detected as reversed or
already applied. We can add that support but for now
we distinguish this by grep'ing the results. We nuke
already applied patches, this typically would come from
linux-next, on linux-stable branches given that there is
no linearity between the two.

To support this change however it means we now have
the double amount of time it takes to apply patches
given that we now need a dry run first. The algorithm
for checking if a patch is reversed only works by
analyzing the first hunk of a patch though so perhaps
what we need on GNU Patch is a check for asking if
a patch is reversed, that would not cause much
overhead here, it would just dry run on the first
hunk by reducing the search space considerably.

Signed-off-by: Luis R. Rodriguez <mcgrof@do-not-panic.com>