serial: Add serial_mvebu_a3700 for Armada 3700 SoC

serial: Add serial_mvebu_a3700 for Armada 3700 SoC

The Armada 3700's UART is a simple serial port. It has a 32 bytes
Tx FIFO and a 64 bytes Rx FIFO integrated. This patch adds support
for this UART including the DEBUG UART functions for very early
debug output.

Signed-off-by: Stefan Roese <[email protected]>
Cc: Nadav Haklai <[email protected]>
Cc: Kostya Porotchkin <[email protected]>
Cc: Wilson Ding <[email protected]>
Cc: Victor Gu <[email protected]>
Cc: Hua Jing <[email protected]>
Cc: Terry Zhou <[email protected]>
Cc: Hanna Hawa <[email protected]>
Cc: Haim Boot <[email protected]>