vfio: platform: add the VFIO PLATFORM module to Kconfig

Enable building the VFIO PLATFORM driver that allows to use Linux platform
devices with VFIO.

Signed-off-by: Antonios Motakis <a.motakis@virtualopensystems.com>
Signed-off-by: Baptiste Reynal <b.reynal@virtualopensystems.com>
Reviewed-by: Eric Auger <eric.auger@linaro.org>
Tested-by: Eric Auger <eric.auger@linaro.org>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

drivers/vfio/platform/Makefile

@@ -0,0 +1,4 @@
+
+vfio-platform-y := vfio_platform.o vfio_platform_common.o
+
+obj-$(CONFIG_VFIO_PLATFORM) += vfio-platform.o