broadcom/bcm5785: Move HAVE_HARD_RESET to southbridge

broadcom/bcm5785: Move HAVE_HARD_RESET to southbridge

No in-tree board using that chipset has it not selected, so move
selection from boards to southbridge.

Change-Id: Id95660f088c8240606d45abf326cd5eefca30da3
Signed-off-by: Patrick Georgi <patrick@georgi-clan.de>
Reviewed-on: http://review.coreboot.org/658
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Tested-by: build bot (Jenkins)