drm: introduce drm_dev_{get/put} functions

Reference counting functions in the kernel typically use get/put suffixes. For
maintaining coding style consistency, introduce drm_dev_{get/put} functions. All
callers of drm_dev_ref() API have been converted in this patch and hence it has
been dropped while the drm_dev_unref() API with non-trivial number of users
remains for compatibility.

The semantic patch scripts/coccinelle/api/drm-get-put.cocci has been updated
with the new helper for conversion of drm_dev_unref() to drm_dev_put()

Signed-off-by: Aishwarya Pant <aishpant@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/6babda56134035a98220d5d37a4fd4048df214ce.1506413698.git.aishpant@gmail.com

scripts/coccinelle/api/drm-get-put.cocci

@@ -50,6 +50,9 @@ expression object;
 |
 - drm_property_unreference_blob(object)
 + drm_property_blob_put(object)
+|
+- drm_dev_unref(object)
++ drm_dev_put(object)
 )
 
 @r depends on report@
@@ -81,6 +84,8 @@ drm_gem_object_unreference_unlocked(object)
 drm_property_unreference_blob@p(object)
 |
 drm_property_reference_blob@p(object)
+|
+drm_dev_unref@p(object)
 )
 
 @script:python depends on report@