arm: add CONFIG_MACH_TYPE setting and documentation

CONFIG_MACH_TYPE is used to set the machine type number in the
common arm code instead of setting it in the board code.
Boards with dynamically discoverable machine types can still set the
machine type number in the board code.
Signed-off-by: NIgor Grinberg <grinberg@compulab.co.il>

README

@@ -442,6 +442,16 @@ The following options need to be configured:
 		crash. This is needed for buggy hardware (uc101) where
 		no pull down resistor is connected to the signal IDE5V_DD7.
 
+		CONFIG_MACH_TYPE	[relevant for ARM only][mandatory]
+
+		This setting is mandatory for all boards that have only one
+		machine type and must be used to specify the machine type
+		number as it appears in the ARM machine registry
+		(see http://www.arm.linux.org.uk/developer/machines/).
+		Only boards that have multiple machine types supported
+		in a single configuration file and the machine type is
+		runtime discoverable, do not have to use this setting.
+
 - vxWorks boot parameters:
 
 		bootvx constructs a valid bootline using the following

arch/arm/lib/board.c

@@ -281,6 +281,10 @@ void board_init_f (ulong bootflag)
 
 	gd->mon_len = _bss_end_ofs;
 
+#ifdef CONFIG_MACH_TYPE
+	gd->bd->bi_arch_number = CONFIG_MACH_TYPE; /* board id for Linux */
+#endif
+
 	for (init_fnc_ptr = init_sequence; *init_fnc_ptr; ++init_fnc_ptr) {
 		if ((*init_fnc_ptr)() != 0) {
 			hang ();