serial: sh-sci: Document remaining FIFO Control Register bits

#define SCIF_DEFAULT_ERROR_MASK (SCIF_PER | SCIF_FER | SCIF_ER | SCIF_BRK)

/* SCFCR (FIFO Control Register) */

#define SCFCR_MCE	0x0008

#define SCFCR_TFRST	0x0004

#define SCFCR_RFRST	0x0002

#define SCFCR_MCE	0x0008		/* Modem Control Enable */

#define SCFCR_TFRST	0x0004		/* Transmit FIFO Data Register Reset */

#define SCFCR_RFRST	0x0002		/* Receive FIFO Data Register Reset */

#define SCFCR_LOOP	(1 << 0)	/* Loopback Test */

/* SCSPTR (Serial Port Register), optional */