vfs_console_context_t struct

This file is to concentrate all the vfs(UART, USB_SERIAL_JTAG, CDCACM) console into one single file. Get the vfs information from their component (i.e. uart_vfs.c), which can help us to output some string to two different ports(i.e both through uart and usb_serial_jtag). Usually, we set a port as primary and another as secondary. For primary, it is used for all the features supported by each vfs implementation, while the secondary is only used for output.