arm/early-printk: add Calxeda Midway UART support

With the help of the previous patches add a stanza to
xen/arch/arm/Rules.mk to specify the UART configuration of the
Calxeda Midway machine.
The information has been taken from the Linux kernel's .dts file.
This can be enabled by adding "CONFIG_EARLY_PRINTK=midway" to
Config.mk.

Signed-off-by: Andre Przywara <andre.przywara@calxeda.com>
Reviewed-by: Julien Grall <julien.grall@linaro.org>
Acked-by: Ian Campbell <ian.campbell@citrix.com>

docs/misc/arm/early-printk.txt

@@ -11,6 +11,7 @@ CONFIG_EARLY_PRINTK=mach
 where mach is the name of the machine:
   - vexpress: printk with pl011 for versatile express
   - exynos5250: printk with the second UART
+  - midway: printk with the pl011 on Calxeda Midway processors
   - fastmodel: printk on ARM Fastmodel software emulators
 
 The base address and baud rate is hardcoded in xen/arch/arm/Rules.mk,

xen/arch/arm/Rules.mk

@@ -59,6 +59,11 @@ EARLY_PRINTK_INIT_UART := y
 EARLY_PRINTK_BAUD := 115200
 EARLY_UART_BASE_ADDRESS := 0x12c20000
 endif
+ifeq ($(CONFIG_EARLY_PRINTK), midway)
+EARLY_PRINTK_INC := pl011
+EARLY_PRINTK_BAUD := 115200
+EARLY_UART_BASE_ADDRESS := 0xfff36000
+endif
 
 ifneq ($(EARLY_PRINTK_INC),)
 EARLY_PRINTK := y