drm/tiny: panel-mipi-dbi: Read I/O supply from DT

To support platforms with a separate I/O voltage supply, set the new
io_regulator property along with the regulator property of the DBI
device. Read the I/O supply from a new "io-supply" device tree
property.
Signed-off-by: Otto Pflüger <otto.pflueger@abscue.de>
Reviewed-by: Noralf Trønnes <noralf@tronnes.org>
Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20221201160245.2093816-3-otto.pflueger@abscue.de

drivers/gpu/drm/tiny/panel-mipi-dbi.c

@@ -294,6 +294,11 @@ static int panel_mipi_dbi_spi_probe(struct spi_device *spi)
 		return dev_err_probe(dev, PTR_ERR(dbidev->regulator),
 				     "Failed to get regulator 'power'\n");
 
+	dbidev->io_regulator = devm_regulator_get(dev, "io");
+	if (IS_ERR(dbidev->io_regulator))
+		return dev_err_probe(dev, PTR_ERR(dbidev->io_regulator),
+				     "Failed to get regulator 'io'\n");
+
 	dbidev->backlight = devm_of_find_backlight(dev);
 	if (IS_ERR(dbidev->backlight))
 		return dev_err_probe(dev, PTR_ERR(dbidev->backlight), "Failed to get backlight\n");