Some versions of SoC MT7621 have three PCI express hosts. Some boards
make use of those PCI through the staging driver mt7621-pci. Recently
PCI support has been removed from MT7621 Soc kernel configuration due
to a build error. This makes imposible to compile staging driver and
produces a regression for gnubee based boards. Enable support for PCI
again but enable it only if staging mt7621-pci driver is selected.

Fixes: c4d48cf5 ("MIPS: ralink: deactivate PCI support for SOC_MT7621")
Cc: Hauke Mehrtens <hauke@hauke-m.de>
Cc: ralf@linux-mips.org
Cc: jhogan@kernel.org
Cc: john@phrozen.org
Cc: NeilBrown <neil@brown.name>
Cc: linux-mips@vger.kernel.org
Signed-off-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Link: https://lore.kernel.org/r/20191019081233.7337-1-sergio.paracuellos@gmail.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>