Add application skeleton for st7789_lcd app

src/application/st7789_lcd/main.c

@@ -0,0 +1,30 @@
+#include <string.h>
+
+#include "app_util_platform.h"
+#include "board.h"
+#include "app_error.h"
+
+#include "driver.h"
+#include "delay.h"
+
+const char buffer[] = "Hello world!\r\n";
+int main(void)
+{
+    unsigned int i = 0;
+    drv_open(&led_1);
+    drv_write(&led_1, "1", 1);
+    drv_open(&spi_0);
+
+    // APP_ERROR_CHECK(NRF_LOG_INIT(NULL));
+    // NRF_LOG_DEFAULT_BACKENDS_INIT();
+
+    // NRF_LOG_INFO("SPI example started.");
+
+    while(1) {
+        drv_write(&spi_0, buffer, sizeof(buffer));
+        // NRF_LOG_FLUSH();
+        char c = (i++ % 2) + 0x30;
+        drv_write(&led_1, &c, 1);
+        delay_ms(200);
+    }
+}