arm: mvebu: turris_omnia: Show MCU type in show_board_info()

Different Turris Omnia HW board revisions contains different MCU.
Show type in show_board_info() to easily identify which MCU is populated.

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