kernel-doc: set verbose mode via environment

Honor the environment variable "KBUILD_VERBOSE=1" (as set by make V=1) to
enable verbose mode in scripts/kernel-doc.  Useful for getting more info and
warnings from kernel-doc.
Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

scripts/kernel-doc

@@ -247,6 +247,10 @@ my ($function, %function_table,%parametertypes,$declaration_purpose);
 my ($type,$declaration_name,$return_type);
 my ($newsection,$newcontents,$prototype,$filelist, $brcount, %source_map);
 
+if (defined($ENV{'KBUILD_VERBOSE'})) {
+	$verbose = "$ENV{'KBUILD_VERBOSE'}";
+}
+
 # Generated docbook code is inserted in a template at a point where
 # docbook v3.1 requires a non-zero sequence of RefEntry's; see:
 # http://www.oasis-open.org/docbook/documentation/reference/html/refentry.html