mkefidisk.sh: add boot log on console

mkefidisk.sh: add boot log on console

Hooking up a serial console is a "developer mode", the chances are pretty good
developers are interested in watching the kernel boot log on the console so
they can spot any problems or diagnose any failed boots (e.g. can't find root
fs).

(From OE-Core rev: d03e399623b9320268a2b56e4928bb7effa9146c)

Signed-off-by: Trevor Woerner <twoerner@gmail.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>