Update LED behavior at powering up

At powering up, both green and red LEDs are on. Only after a successful
boot the LED status will change to green. This is used to indicate the
emergency mode.

Also update the u-boot console message of MMC capacity detection.

Bug: 171704186
Change-Id: I09b22ba9c629cac501ee4c2e9a2f792cfe93dd59