serial: 8250_omap: workaround module disable errata on dra7x SoCs

Due to Advisory 21 as documented in AM437x errata document,
UART module cannot be disabled once DMA is used. The only
workaround is to softreset the module before disabling it.

DRA7x UARTs are compatible to AM437x UARTs in terms of
this errata and prescribed workaround.

Enable usage of workaround for this errata on DRA7x SoCs.
Signed-off-by: Sekhar Nori <nsekhar@ti.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Reviewed-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/serial/omap_serial.txt

@@ -6,6 +6,7 @@ Required properties:
 - compatible : should be "ti,omap4-uart" for OMAP4 controllers
 - compatible : should be "ti,am4372-uart" for AM437x controllers
 - compatible : should be "ti,am3352-uart" for AM335x controllers
+- compatible : should be "ti,dra742-uart" for DRA7x controllers
 - reg : address and length of the register space
 - interrupts or interrupts-extended : Should contain the uart interrupt
                                       specifier or both the interrupt

drivers/tty/serial/8250/8250_omap.c

@@ -1082,6 +1082,7 @@ static const struct of_device_id omap8250_dt_ids[] = {
 	{ .compatible = "ti,omap4-uart" },
 	{ .compatible = "ti,am3352-uart", .data = &am3352_habit, },
 	{ .compatible = "ti,am4372-uart", .data = &am4372_habit, },
+	{ .compatible = "ti,dra742-uart", .data = &am4372_habit, },
 	{},
 };
 MODULE_DEVICE_TABLE(of, omap8250_dt_ids);