escc: send software reset command before configuring the port

According to the ESCC datasheet all register values are undetermined until an
explicit reset command is sent. This is required to fix an issue with QEMU's
ESCC device to ensure that the registers are set to default values if the
default power-on values are changed.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>