Use stdbool more widely

We already use the C99 bool type from stdbool.h in a few places.  However
there are many other places we represent boolean values as plain ints.
This patch changes that.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
diff --git a/dtc-lexer.l b/dtc-lexer.l
index 3b41bfc..369407a 100644
--- a/dtc-lexer.l
+++ b/dtc-lexer.l
@@ -61,7 +61,7 @@
 				BEGIN(V1); \
 
 static void push_input_file(const char *filename);
-static int pop_input_file(void);
+static bool pop_input_file(void);
 %}
 
 %%
@@ -238,13 +238,13 @@
 }
 
 
-static int pop_input_file(void)
+static bool pop_input_file(void)
 {
 	if (srcfile_pop() == 0)
-		return 0;
+		return false;
 
 	yypop_buffer_state();
 	yyin = current_srcfile->f;
 
-	return 1;
+	return true;
 }