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/src/main.c

@@ -0,0 +1,63 @@
+#include "tos_k.h"
+
+#include "bsp_clk.h"
+#include "bsp_delay.h"
+#include "bsp_led.h"
+#include "bsp_beep.h"
+#include "bsp_key.h"
+#include "bsp_int.h"
+#include "bsp_uart.h"
+#include "bsp_exit.h"
+#include "bsp_epittimer.h"
+
+void task1_entry(void *arg)
+{
+    while (1) {
+        printf("task1\r\n");
+        tos_task_delay(2000);
+    }
+}
+
+void task2_entry(void *arg)
+{
+    while (1) {
+        printf("task2\r\n");
+        tos_task_delay(3000);
+    }
+}
+
+k_task_t task1;
+k_stack_t task1_stack[512];
+
+k_task_t task2;
+k_stack_t task2_stack[512];
+
+int main(void)
+{
+    unsigned char state = OFF;
+
+    uart_init();
+    led_init();
+    beep_init();
+    key_init();
+
+    tos_knl_init();
+
+    tos_task_create(&task1, "task1", task1_entry, NULL,
+                        4,
+                        task1_stack, sizeof(task1_stack),
+                        0);
+    tos_task_create(&task2, "task2", task2_entry, NULL,
+                        4,
+                        task2_stack, sizeof(task2_stack),
+                        0);
+
+    tos_knl_start();
+
+    while (1) {
+        delay(3000);
+    }
+
+    return 0;
+}
+