Implementation is simple, just wait for the TX FIFO to be empty.
Without this patch TF-A on A3720 truncate the last line:
NOTICE: BL31: Built : 16:1
With this patch TF-A on A3720 print correctly also the last line:
NOTICE: BL31: Built : 19:03:31, Dec 23 2020
Signed-off-by: Pali Rohár <pali@kernel.org>
Change-Id: I2f2ea42beab66ba132afdb400ca7898c5419db09