rework structure

hifive1-vp/hello/bsp/include/sifive/devices/uart.h

@@ -0,0 +1,27 @@
+// See LICENSE for license details.
+
+#ifndef _SIFIVE_UART_H
+#define _SIFIVE_UART_H
+
+/* Register offsets */
+#define UART_REG_TXFIFO         0x00
+#define UART_REG_RXFIFO         0x04
+#define UART_REG_TXCTRL         0x08
+#define UART_REG_RXCTRL         0x0c
+#define UART_REG_IE             0x10
+#define UART_REG_IP             0x14
+#define UART_REG_DIV            0x18
+
+/* TXCTRL register */
+#define UART_TXEN               0x1
+#define UART_TXWM(x)            (((x) & 0xffff) << 16)
+
+/* RXCTRL register */
+#define UART_RXEN               0x1
+#define UART_RXWM(x)            (((x) & 0xffff) << 16)
+
+/* IP register */
+#define UART_IP_TXWM            0x1
+#define UART_IP_RXWM            0x2
+
+#endif /* _SIFIVE_UART_H */