vfio: platform: introduce vfio-platform-base module

To prepare for vfio platform reset rework let's build
vfio_platform_common.c and vfio_platform_irq.c in a separate
module from vfio-platform and vfio-amba. This makes possible
to have separate module inits and works around a race between
platform driver init and vfio reset module init: that way we
make sure symbols exported by base are available when vfio-platform
driver gets probed.

The open/release being implemented in the base module, the ref
count is applied to the parent module instead.

Signed-off-by: Eric Auger <eric.auger@linaro.org>
Suggested-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
diff --git a/drivers/vfio/platform/Makefile b/drivers/vfio/platform/Makefile
index 9ce8afe..41a6224 100644
--- a/drivers/vfio/platform/Makefile
+++ b/drivers/vfio/platform/Makefile
@@ -1,10 +1,12 @@
-
-vfio-platform-y := vfio_platform.o vfio_platform_common.o vfio_platform_irq.o
+vfio-platform-base-y := vfio_platform_common.o vfio_platform_irq.o
+vfio-platform-y := vfio_platform.o
 
 obj-$(CONFIG_VFIO_PLATFORM) += vfio-platform.o
+obj-$(CONFIG_VFIO_PLATFORM) += vfio-platform-base.o
 obj-$(CONFIG_VFIO_PLATFORM) += reset/
 
 vfio-amba-y := vfio_amba.o
 
 obj-$(CONFIG_VFIO_AMBA) += vfio-amba.o
+obj-$(CONFIG_VFIO_AMBA) += vfio-platform-base.o
 obj-$(CONFIG_VFIO_AMBA) += reset/