add cortex-v7a support

How To Run:
    see TencentOS-tiny\board\ALPHA_I.MX_emmc_256ddr\README.md

TODO Next:
1. VFP support
2. fault diagnosis support
3. qemu vexpress ca9 support
4. raspberry pi support
5. SMP support

board/ALPHA_I.MX_emmc_256ddr/stdio/lib/printf.c

@@ -0,0 +1,60 @@
+#include "vsprintf.h"
+#include "string.h"
+#include "printf.h"
+#include "bsp_uart.h"
+
+extern void uart_putc(unsigned char c);
+extern unsigned char uart_getc(void);
+
+#define	OUTBUFSIZE	1024
+#define	INBUFSIZE	1024
+
+
+static char g_pcOutBuf[OUTBUFSIZE];
+static char g_pcInBuf[INBUFSIZE];
+
+
+int printf(const char *fmt, ...)
+{
+    int i;
+    int len;
+    va_list args;
+
+    va_start(args, fmt);
+    len = vsprintf(g_pcOutBuf,fmt,args);
+    va_end(args);
+    for (i = 0; i < strlen(g_pcOutBuf); i++)
+    {
+        uart_putc(g_pcOutBuf[i]);
+    }
+    return len;
+}
+
+int scanf(const char * fmt, ...)
+{
+    int i = 0;
+    unsigned char c;
+    va_list args;
+
+    while(1)
+    {
+        c = uart_getc();
+        uart_putc(c);
+        if((c == 0x0d) || (c == 0x0a))
+        {
+            g_pcInBuf[i] = '\0';
+            break;
+        }
+        else
+        {
+            g_pcInBuf[i++] = c;
+        }
+    }
+
+    va_start(args,fmt);
+    i = vsscanf(g_pcInBuf,fmt,args);
+    va_end(args);
+
+    return i;
+}
+