Since commit d41e6858 ("MIPS: Kconfig: Set default MIPS system type
as generic") changed the default MIPS platform to the "generic"
platform, which uses PCI_DRIVERS_GENERIC instead of PCI_DRIVERS_LEGACY,
various files in drivers/ssb/ have failed to build.

This is particularly due to the existence of struct pci_controller being
dependent on PCI_DRIVERS_LEGACY since commit c5611df9 ("MIPS: PCI:
Introduce CONFIG_PCI_DRIVERS_LEGACY"), so add that dependency to Kconfig
to prevent these files being built for the "generic" platform including
all{yes,mod}config builds.

Fixes: c5611df9

 ("MIPS: PCI: Introduce CONFIG_PCI_DRIVERS_LEGACY")
Signed-off-by: James Hogan <jhogan@kernel.org>
Cc: Michael Buesch <m@bues.ch>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Paul Burton <paul.burton@mips.com>
Cc: Matt Redfearn <matt.redfearn@imgtec.com>
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: linux-wireless@vger.kernel.org
Cc: linux-mips@linux-mips.org
Tested-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>