amd/sb800: Move HAVE_HARD_RESET to southbridge

amd/sb800: Move HAVE_HARD_RESET to southbridge

No in-tree board using that chipset has it not selected, so move
selection from boards to southbridge. (cimx/sb800 is a "different"
chipset)

Change-Id: If7cf2a141a1f2df60f687c51fbd760aa405c8480
Signed-off-by: Patrick Georgi <patrick@georgi-clan.de>
Reviewed-on: http://review.coreboot.org/666
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Tested-by: build bot (Jenkins)