serial: arm_dcc: Remove CONFIG_ARM_DCC_MULTI option

serial: arm_dcc: Remove CONFIG_ARM_DCC_MULTI option

CONFIG_ARM_DCC_MULTI should be also removed in the patch
"serial: Remove CONFIG_SERIAL_MULTI from serial drivers"
(sha1: a3827250606895ec2dd4b8d867342b7cabf3692f)
Because the driver defines serial_* functions
which cause conflict with serial.c (multiple definition of serial_*)

Removing CONFIG_SERIAL_MULTI function also require to define
default_serial_console for cases where another serial driver
is not available in the system.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Acked-by: Marek Vasut <marex@denx.de>