improved uart character printing and poweroff/restart

src/kernel/kernel.c

@@ -1,11 +1,9 @@
 #include <stdint.h>
 #include <stddef.h>
+#include <drivers/uart.h>
+#include <syscon/syscon.h>
 
 void kmain() {
-    char *uart = (char *)0x10000000;
-    char *msg = "Hello, OS World!\n";
-    
-    for (int i = 0; msg[i] != '\0'; i++) {
-        *uart = msg[i]; // Write each character to the UART
-    }
+    kprint("Hello, OS World!\n");
+    poweroff();
 }