Squash commits for public release

boot/arm64/prekernel/drivers/uart.c

@@ -0,0 +1,23 @@
+#include "uart.h"
+#include <libboot/devtree/devtree.h>
+
+volatile uint32_t* output = NULL;
+
+void uart_init()
+{
+    devtree_entry_t* dev = devtree_find_device("uart");
+    if (!dev) {
+        return;
+    }
+    output = (uint32_t*)dev->region_base;
+}
+
+int uart_write(uint8_t data)
+{
+    if (!output) {
+        return 1;
+    }
+
+    *output = data;
+    return 0;
+}