soc/amd/common: Add weak call for platform PCIE slot reset

Since it is fairly uncommon, add a weak call that may be done by
the platform if it has the support.

BUG=b:66690176
BRANCH=none
TEST=coreboot builds.

Change-Id: I50008da6f85039a428184bf9e7642c0aa6610247
Signed-off-by: Marc Jones <marcj303@gmail.com>
Reviewed-on: https://review.coreboot.org/22193
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
2 files changed