drm/encoder: Add macro drmm_plain_encoder_alloc()

This performs the same operation as drmm_encoder_alloc(), but
only allocates and returns a struct drm_encoder instance.

v4: Rename macro drmm_plain_encoder_alloc() and move to
    <drm/drm_encoder.h>. Since it's not "simple" anymore it
    will now take funcs/name arguments as well.
Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210327115742.18986-3-paul@crapouillou.net

include/drm/drm_encoder.h

@@ -224,6 +224,24 @@ void *__drmm_encoder_alloc(struct drm_device *dev,
 				      offsetof(type, member), funcs, \
 				      encoder_type, name, ##__VA_ARGS__))
 
+/**
+ * drmm_plain_encoder_alloc - Allocate and initialize an encoder
+ * @dev: drm device
+ * @funcs: callbacks for this encoder (optional)
+ * @encoder_type: user visible type of the encoder
+ * @name: printf style format string for the encoder name, or NULL for default name
+ *
+ * This is a simplified version of drmm_encoder_alloc(), which only allocates
+ * and returns a struct drm_encoder instance, with no subclassing.
+ *
+ * Returns:
+ * Pointer to the new drm_encoder struct, or ERR_PTR on failure.
+ */
+#define drmm_plain_encoder_alloc(dev, funcs, encoder_type, name, ...) \
+	((struct drm_encoder *) \
+	 __drmm_encoder_alloc(dev, sizeof(struct drm_encoder), \
+			      0, funcs, encoder_type, name, ##__VA_ARGS__))
+
 /**
  * drm_encoder_index - find the index of a registered encoder
  * @encoder: encoder to find index for