arm: a37xx: Disable CONFIG_DEBUG_UART_ANNOUNCE

After next branch was merged to v2022.01 release, U-Boot on A3720 started
printing "<debug_uart>" line on UART during booting. There is no need to
print this debug line by default, so disable it via config option
CONFIG_DEBUG_UART_ANNOUNCE in all config files for Armada 3720 boards.

Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Stefan Roese <sr@denx.de>