FASTBOOT: Add a printf log and a command to dump it

For serial-less devices, it's useful to be able to see
the console messages that might have been dumped by
the bootloader.  Add a non-circuluar log buffer (default
size of 4000 bytes, can be overridden by board config) that
all post relocate printfs get appended to.

To dump the contents, do 'fastboot oem log'

Change-Id: Ie63baf86f6380bbe4851f7d062d9f9013d388865
Signed-off-by: Mike J. Chen <[email protected]>
1 file changed