Fix early uart on malta, now malta board can print things!

Signed-off-by: Harry Chen <i@harrychen.xyz>

kernel/Makefile

@@ -127,7 +127,7 @@ else ifeq ($(arch), mipsel)
 ifeq ($(board), malta)
 qemu_opts += \
 	-machine $(board) \
-	-serial none -serial none -serial mon:stdio \
+	-serial mon:stdio \
 	-kernel $(kernel_img)
 endif
 endif

kernel/src/arch/mipsel/board/malta/device.dts

@@ -24,6 +24,12 @@
 		reg = <0x00000000 0x10000000>;
 	};
 
+	uart0: serial@b80003f8 {
+		compatible = "ns16550a";
+		reg = <0xb80003f8 0x8>;
+		clock-frequency = <1843200>;
+	};
+
 	uart2: serial@bf000900 {
 		compatible = "ns16550a";
 		reg = <0xbf000900 0x40>;

kernel/src/arch/mipsel/board/malta/mod.rs

@@ -10,7 +10,7 @@ pub mod console;
 /// Initialize serial port first
 pub fn init_serial_early() {
     assert_has_not_been_called!("board::init must be called only once");
-    serial::init(0xbf000900);
+    serial::init(0xb80003f8);
     println!("Hello QEMU Malta!");
 }