ARM: PL011: add DMA burst threshold support for ST variants

ST Micro variants has some specific dma burst threshold compensation,
which allows them to make better use of a DMA controller.  Add support
to set this up.

Based on a patch from Linus Walleij.

Acked-by: Linus Walleij <linus.walleij@stericsson.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
diff --git a/include/linux/amba/serial.h b/include/linux/amba/serial.h
index 577f22e..5479fdc 100644
--- a/include/linux/amba/serial.h
+++ b/include/linux/amba/serial.h
@@ -113,6 +113,21 @@
 #define UART01x_LCRH_PEN	0x02
 #define UART01x_LCRH_BRK	0x01
 
+#define ST_UART011_DMAWM_RX_1	(0 << 3)
+#define ST_UART011_DMAWM_RX_2	(1 << 3)
+#define ST_UART011_DMAWM_RX_4	(2 << 3)
+#define ST_UART011_DMAWM_RX_8	(3 << 3)
+#define ST_UART011_DMAWM_RX_16	(4 << 3)
+#define ST_UART011_DMAWM_RX_32	(5 << 3)
+#define ST_UART011_DMAWM_RX_48	(6 << 3)
+#define ST_UART011_DMAWM_TX_1	0
+#define ST_UART011_DMAWM_TX_2	1
+#define ST_UART011_DMAWM_TX_4	2
+#define ST_UART011_DMAWM_TX_8	3
+#define ST_UART011_DMAWM_TX_16	4
+#define ST_UART011_DMAWM_TX_32	5
+#define ST_UART011_DMAWM_TX_48	6
+
 #define UART010_IIR_RTIS	0x08
 #define UART010_IIR_TIS		0x04
 #define UART010_IIR_RIS		0x02