am335x, guardian: boot stage feedback in headless mode

This patch enables the guardian board to provide feedback
  about the boot stage in headless mode. The on-board led
  would behave in the following pattern

    * U-boot -> GLOW LED
    * Linux  -> BLINK LED [HEART-BEAT PATTERN]

Signed-off-by: Moses Christopher <BollavarapuMoses.Christopher@in.bosch.com>