devkit3250: add Timll DevKit3250 board initial support

This change adds a basic support for Embest/Timll DevKit3250 board,
NOR and UART are the only supported peripherals for a moment. The board
doesn't require low-level init, because the initial SDRAM and GPIO
configuration is performed during kickstart bootloader execution.

Signed-off-by: Vladimir Zapolskiy <vz@mleia.com>
Cc: Albert ARIBAUD <albert.u.boot@aribaud.net>
Acked-by: Marek Vasut <marek.vasut@gmail.com>