drm/vc4: hdmi: Deal with multiple debugfs files

The HDMI driver was registering a single debugfs file so far with the name
hdmi_regs.

Obviously, this is not going to work anymore when will have multiple HDMI
controllers since we will end up trying to register two files with the same
name.

Let's use the variant to avoid that name conflict.

Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Tested-by: Chanwoo Choi <cw00.choi@samsung.com>
Tested-by: Hoegeun Kwon <hoegeun.kwon@samsung.com>
Tested-by: Stefan Wahren <stefan.wahren@i2se.com>
Reviewed-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Link: https://patchwork.freedesktop.org/patch/msgid/9505c1eb40b3ef3709277bf9e8af77917b249c32.1599120059.git-series.maxime@cerno.tech

drivers/gpu/drm/vc4/vc4_hdmi.h

@@ -30,6 +30,9 @@ struct vc4_hdmi_variant {
 	/* Encoder Type for that controller */
 	enum vc4_encoder_type encoder_type;
 
+	/* Filename to expose the registers in debugfs */
+	const char *debugfs_name;
+
 	/* List of the registers available on that variant */
 	const struct vc4_hdmi_register *registers;