drm/nouveau/pm: rename from perfmon (no binary change)

Switch to NVIDIA's name for the device.

The namespace of NVKM is being changed to nvkm_ instead of nouveau_,
which will be used for the DRM part of the driver.  This is being
done in order to make it very clear as to what part of the driver a
given symbol belongs to, and as a minor step towards splitting the
DRM driver out to be able to stand on its own (for virt).

Because there's already a large amount of churn here anyway, this is
as good a time as any to also switch to NVIDIA's device and chipset
naming to ease collaboration with them.

A comparison of objdump disassemblies proves no code changes.

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
diff --git a/drivers/gpu/drm/nouveau/nvkm/engine/device/gm100.c b/drivers/gpu/drm/nouveau/nvkm/engine/device/gm100.c
index e7289fd..2ea1dbc 100644
--- a/drivers/gpu/drm/nouveau/nvkm/engine/device/gm100.c
+++ b/drivers/gpu/drm/nouveau/nvkm/engine/device/gm100.c
@@ -53,7 +53,7 @@
 #include <engine/msvld.h>
 #include <engine/vp.h>
 #include <engine/ppp.h>
-#include <engine/perfmon.h>
+#include <engine/pm.h>
 
 int
 gm100_identify(struct nouveau_device *device)