drivers: ti: uart: Add TI specific 16550 initialization

On TI platforms the UART is disabled by default and must be explicitly
enabled using the MDR1 register.

NOTE: The original definition of
http://www.ti.com/lit/ds/symlink/pc16550d.pdf has no MDR register, but
many TI SoCs implementing 16550 do have a quirky MDR register
implemented. So, this should be enabled with TI_16550_MDR_QUIRK

NOTE: In such implementation, the CSR register does not exist.

Signed-off-by: Benjamin Fair <b-fair@ti.com>
Signed-off-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Andrew F. Davis <afd@ti.com>
diff --git a/include/drivers/ti/uart/uart_16550.h b/include/drivers/ti/uart/uart_16550.h
index 9eba41a..b00f664 100644
--- a/include/drivers/ti/uart/uart_16550.h
+++ b/include/drivers/ti/uart/uart_16550.h
@@ -23,6 +23,8 @@
 #define UARTMSR			0x18
 #define UARTSPR			0x1c
 #define UARTCSR			0x20
+/* Some instances have MDR1 defined as well */
+#define UARTMDR1		0x20
 #define UARTRXFIFOCFG		0x24
 #define UARTMIE			0x28
 #define UARTVNDR		0x2c