drm/xe/vm: move xe_svm_init() earlier

In the Linux kernel, the following vulnerability has been resolved:

drm/xe/vm: move xe_svm_init() earlier

In xe_vm_close_and_put() we need to be able to call xe_svm_fini(),

however during vm creation we can call this on the error path, before

having actually initialised the svm state, leading to various splats

followed by a fatal NPD.

(cherry picked from commit 4f296d77cf49fcb5f90b4674123ad7f3a0676165)