Status LED
  ========================================
  
  This README describes the status LED API.
  
  The API is defined by the include file include/status_led.h
  
  The first step is to define CONFIG_STATUS_LED in the board config file.
  
  If the LED support is only for a single board, define CONFIG_BOARD_SPECIFIC_LED
  in the board config file.

  At a minimum, these macros must be defined at

  STATUS_LED_BIT
  STATUS_LED_STATE
  STATUS_LED_PERIOD
  
  If there are multiple status LED's define
  STATUS_LED_BIT<n>
  STATUS_LED_STATE<n>
  STATUS_LED_PERIOD<n>

  Where <n> can a integer 1 through 3.

  
  STATUS_LED_BIT is passed into the __led_* functions to identify which LED is
  being acted on.  As such, the value choose must be unique with with respect to
  the other STATUS_LED_BIT's.  Mapping the value to a physical LED is the
  reponsiblity of the __led_* function.
  
  STATUS_LED_STATE is the initial state of the LED. It should be set to one of
  these values: STATUS_LED_OFF or STATUS_LED_ON.
  
  STATUS_LED_PERIOD is how long is the LED blink period.  This usually set to
  (CONFIG_SYS_HZ / <N>) where <N> is the frequency of the blink. Typical values
  range from 2 to 10.
  
  Some other LED macros
  
  STATUS_LED_BOOT is the LED to light when the board is booting.  This must be a

  valid STATUS_LED_BIT value.

  
  STATUS_LED_RED is the red LED.  It is used signal errors. This must be a valid
  STATUS_LED_BIT value. Other similar color LED's are STATUS_LED_YELLOW and

  STATUS_LED_BLUE.

  
  These board must define these functions
  
  __led_init is called once to initialize the LED to STATUS_LED_STATE. One time
  start up code should be placed here.

  __led_set is called to change the state of the LED.

  
  __led_toggle is called to toggle the current state of the LED.
  
  Colour LED
  ========================================

  Colour LED's are at present only used by ARM.

  
  The functions names explain their purpose.
  
  coloured_LED_init
  red_LED_on
  red_LED_off
  green_LED_on
  green_LED_off
  yellow_LED_on
  yellow_LED_off
  blue_LED_on
  blue_LED_off

  These are weakly defined in arch/arm/lib/board.c to noops. Where applicable, define

  these functions in the board specific source.
  
  TBD : Describe older board dependent macros similar to what is done for
  CONFIG_TQM8xxL.
  
  TBD : Describe general support via asm/status_led.h