scripts: kernel-doc: try to use c:function if possible

There are a few namespace clashes by using c:macro everywhere:

basically, when using it, we can't have something like:

	.. c:struct:: pwm_capture

	.. c:macro:: pwm_capture

So, we need to use, instead:

	.. c:function:: int pwm_capture (struct pwm_device * pwm, struct pwm_capture * result, unsigned long timeout)

for the function declaration.

The kernel-doc change was proposed by Jakob Lykke Andersen here:

	https://github.com/jakobandersen/linux_docs/commit/6fd2076ec001cca7466857493cd678df4dfe4a65

Although I did a different implementation.
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

scripts/kernel-doc

@@ -917,6 +917,7 @@ sub output_function_rst(%) {
     my ($parameter, $section);
     my $oldprefix = $lineprefix;
     my $start = "";
+    my $is_macro = 0;
 
     if ($sphinx_major < 3) {
 	if ($args{'typedef'}) {
@@ -926,11 +927,17 @@ sub output_function_rst(%) {
 	    $lineprefix = "";
 	    output_highlight_rst($args{'purpose'});
 	    $start = "\n\n**Syntax**\n\n  ``";
+	    $is_macro = 1;
 	} else {
 	    print ".. c:function:: ";
 	}
     } else {
-	print ".. c:macro:: ". $args{'function'} . "\n\n";
+	if ($args{'typedef'} || $args{'functiontype'} eq "") {
+	    $is_macro = 1;
+	    print ".. c:macro:: ". $args{'function'} . "\n\n";
+	} else {
+	    print ".. c:function:: ";
+	}
 
 	if ($args{'typedef'}) {
 	    print_lineno($declaration_start_line);
@@ -939,7 +946,7 @@ sub output_function_rst(%) {
 	    output_highlight_rst($args{'purpose'});
 	    $start = "\n\n**Syntax**\n\n  ``";
 	} else {
-	    print "``";
+	    print "``" if ($is_macro);
 	}
     }
     if ($args{'functiontype'} ne "") {
@@ -964,14 +971,12 @@ sub output_function_rst(%) {
 	    print $type;
 	}
     }
-    if ($args{'typedef'}) {
-	print ");``\n\n";
+    if ($is_macro) {
+	print ")``\n\n";
     } else {
-	if ($sphinx_major < 3) {
-	    print ")\n\n";
-	} else {
-	    print ")``\n";
-	}
+	print ")\n\n";
+    }
+    if (!$args{'typedef'}) {
 	print_lineno($declaration_start_line);
 	$lineprefix = "   ";
 	output_highlight_rst($args{'purpose'});