arm: cut bootloader dependency on uart stuff

arm/bootloader.cc

@@ -1,9 +1,24 @@
 #include <cstdint>
 
 #include "gpio.h"
-#include "uart.h"
+#include "xuartlite.h"
 
 namespace {
+constexpr uintptr_t kUart0BaseAddress = 0x40001000;
+XUartLite uart0_inst;
+XUartLite_Config uart0_config = {
+    .DeviceId = 0,
+    .RegBaseAddr = kUart0BaseAddress,
+    .BaudRate = 115200,
+    .UseParity = false,
+    .DataBits = 8,
+};
+
+XUartLite* uart0 = &uart0_inst;
+
+void InitUarts() {
+    XUartLite_CfgInitialize(uart0, &uart0_config, uart0_config.RegBaseAddr);
+}
 
 uint8_t UartRead() {
     uint8_t c;
@@ -25,7 +40,6 @@ uint32_t UartRead32() {
 
     return val;
 }
-
 }  // namespace
 
 int main() {