Replace the unconditional sleep "until the board comes up" by the
detection of the fastboot-driver message. This shortens the total boot
time and reveals U-boots initial output, e.g., messages reporting
trouble with bringing up the fastboot driver.
The success messages of different versions of the fastboot tool
are printed in different upper/lower case. Tolerate both.
The patch also removes a few superfluous semicolons.
This patch lifts the limitation for 32-bit ARM platforms and makes the
parameter --load-fastboot-device optional. If only one device is
present, it can be omitted.
Fixes#4232
