SSB: Kconfig: Amend SSB_EMBEDDED dependencies

SSB: Kconfig: Amend SSB_EMBEDDED dependencies

SSB_EMBEDDED needs functions from driver_pcicore which are only
available if SSD_DRIVER_HOSTMODE is selected so make it
depend on that symbol.

Fixes the following linking problem:

drivers/ssb/embedded.c:202:
undefined reference to `ssb_pcicore_plat_dev_init'
drivers/built-in.o: In function `ssb_pcibios_map_irq':
drivers/ssb/embedded.c:247:
undefined reference to `ssb_pcicore_pcibios_map_irq'

Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
Acked-by: Steven J. Hill <Steven.Hill@imgtec.com>
Cc: sibyte-users@bitmover.com
Cc: netdev@vger.kernel.org
Cc: Michael Buesch <m@bues.ch>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/5484/
Acked-by: Florian Fainelli <florian@openwrt.org>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>