checkpatch: add a checkpatch warning for new uses of __initcall().

[apw@shadowen.org: generalise pattern and add tests]
Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Andy Whitcroft <apw@shadowen.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

scripts/checkpatch.pl

@@ -2108,6 +2108,10 @@ sub process {
 		if ($line =~ /\bsimple_(strto.*?)\s*\(/) {
 			WARN("consider using strict_$1 in preference to simple_$1\n" . $herecurr);
 		}
+# check for __initcall(), use device_initcall() explicitly please
+		if ($line =~ /^.\s*__initcall\s*\(/) {
+			WARN("please use device_initcall() instead of __initcall()\n" . $herecurr);
+		}
 
 # use of NR_CPUS is usually wrong
 # ignore definitions of NR_CPUS and usage to define arrays as likely right