serial: 8250_omap: Add support for AM654 UART controller

AM654 uses a UART controller that is compatible (partially) with
existing 8250 UART, however, has a few differences with respect to DMA
support and control paths. Introduce a base definition that allows us
to build up the differences in follow on patches.

Cc: Sekhar Nori <[e-mail]>
Cc: Vignesh R <[e-mail]>
Signed-off-by: Nishanth Menon <[e-mail]>
Acked-by: Tony Lindgren <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

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

···
 static const u8 dra742_habit = UART_ERRATA_CLOCK_DISABLE;
 
 static const struct of_device_id omap8250_dt_ids[] = {
+	{ .compatible = "ti,am654-uart" },
 	{ .compatible = "ti,omap2-uart" },
 	{ .compatible = "ti,omap3-uart" },
 	{ .compatible = "ti,omap4-uart", .data = &omap4_habit, },