checkpatch: add PREFER_IS_ENABLED test

Using #if defined CONFIG_<FOO> || defined CONFIG_<FOO>_MODULE is
more verbose than necessary and IS_ENABLED(CONFIG_<FOO>) is preferred.

So add a test and a message for it.

--fix it to if desired.

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

scripts/checkpatch.pl

@@ -5637,6 +5637,16 @@ sub process {
 			}
 		}
 
+# check for #if defined CONFIG_<FOO> || defined CONFIG_<FOO>_MODULE
+		if ($line =~ /^\+\s*#\s*if\s+defined(?:\s*\(?\s*|\s+)(CONFIG_[A-Z_]+)\s*\)?\s*\|\|\s*defined(?:\s*\(?\s*|\s+)\1_MODULE\s*\)?\s*$/) {
+			my $config = $1;
+			if (WARN("PREFER_IS_ENABLED",
+				 "Prefer IS_ENABLED(<FOO>) to CONFIG_<FOO> || CONFIG_<FOO>_MODULE\n" . $herecurr) &&
+			    $fix) {
+				$fixed[$fixlinenr] = "\+#if IS_ENABLED($config)";
+			}
+		}
+
 # check for case / default statements not preceded by break/fallthrough/switch
 		if ($line =~ /^.\s*(?:case\s+(?:$Ident|$Constant)\s*|default):/) {
 			my $has_break = 0;