Kernel: Add kernelearlyputstr and use it in dbgln in very-early boot

This variant of dbgputstr does not lock the global log lock, as it is
called before the current or any other processor was initialized,
meaning that:
A) The $gs base was not setup yet, so we cannot enter into critical
   sections, and as a result we cannot use SpinLocks
B) No other processors may try to print at the same time anyway

AK/Format.cpp

@@ -817,6 +817,14 @@ void vdbgln(StringView fmtstr, TypeErasedFormatParams& params)
 
     const auto string = builder.string_view();
 
+#ifdef __serenity__
+#    ifdef KERNEL
+    if (!Kernel::Processor::is_initialized()) {
+        kernelearlyputstr(string.characters_without_null_termination(), string.length());
+        return;
+    }
+#    endif
+#endif
     dbgputstr(string.characters_without_null_termination(), string.length());
 }
 

Kernel/kprintf.cpp

@@ -188,3 +188,14 @@ extern "C" void kernelcriticalputstr(const char* characters, size_t length)
     for (size_t i = 0; i < length; ++i)
         critical_console_out(characters[i]);
 }
+
+extern "C" void kernelearlyputstr(const char* characters, size_t length)
+{
+    if (!characters)
+        return;
+    // NOTE: We do not lock the log lock here, as this function is called before this or any other processor was initialized, meaning:
+    //  A) The $gs base was not setup yet, so we cannot enter into critical sections, and as a result we cannot use SpinLocks
+    //  B) No other processors may try to print at the same time anyway
+    for (size_t i = 0; i < length; ++i)
+        internal_dbgputch(characters[i]);
+}

Kernel/kstdio.h

@@ -14,6 +14,7 @@ void dbgputch(char);
 void dbgputstr(const char*, size_t);
 void kernelputstr(const char*, size_t);
 void kernelcriticalputstr(const char*, size_t);
+void kernelearlyputstr(const char*, size_t);
 int snprintf(char* buf, size_t, const char* fmt, ...) __attribute__((format(printf, 3, 4)));
 void set_serial_debug(bool on_or_off);
 int get_serial_debug();