drivers: serial8250_uart: use 32-bit accesses to the uart registers

Due to hardware design, some platforms can't access the peripheral IO
registers once a byte(8-bit) but once a word(32-bit). Obviously, using
32-bit accesses to the registers is more flexible for other plaforms
to use serial8250 uart.

Signed-off-by: Joseph Chen <chenjh@rock-chips.com>

core/drivers/serial8250_uart.c

@@ -63,7 +63,7 @@ static void serial8250_uart_flush(struct serial_chip *chip)
 	vaddr_t base = chip_to_base(chip);
 
 	while (1) {
-		uint8_t state = read8(base + UART_LSR);
+		uint32_t state = read32(base + UART_LSR);
 
 		/* Wait until transmit FIFO is empty */
 		if ((state & LSR_EMPTY) == LSR_EMPTY)
@@ -86,7 +86,7 @@ static int serial8250_uart_getchar(struct serial_chip *chip)
 		/* Transmit FIFO is empty, waiting again */
 		;
 	}
-	return read8(base + UART_RHR);
+	return read32(base + UART_RHR);
 }
 
 static void serial8250_uart_putc(struct serial_chip *chip, int ch)
@@ -96,7 +96,7 @@ static void serial8250_uart_putc(struct serial_chip *chip, int ch)
 	serial8250_uart_flush(chip);
 
 	/* Write out character to transmit FIFO */
-	write8(ch, base + UART_THR);
+	write32(ch, base + UART_THR);
 }
 
 static const struct serial_ops serial8250_uart_ops = {