iommufd: Add missing IOMMUFD_DRIVER kconfig for the selftest

Some kconfigs don't automatically include this symbol which results in sub
functions for some of the dirty tracking related things that are
non-functional. Thus the test suite will fail. select IOMMUFD_DRIVER in
the IOMMUFD_TEST kconfig to fix it.

Fixes: a9af47e3 ("iommufd/selftest: Test IOMMU_HWPT_GET_DIRTY_BITMAP")
Link: https://lore.kernel.org/r/20240327182050.GA1363414@ziepe.caTested-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

drivers/iommu/iommufd/Kconfig

@@ -37,6 +37,7 @@ config IOMMUFD_TEST
 	depends on DEBUG_KERNEL
 	depends on FAULT_INJECTION
 	depends on RUNTIME_TESTING_MENU
+	select IOMMUFD_DRIVER
 	default n
 	help
 	  This is dangerous, do not enable unless running