coccinelle: Add rules to find str_plural() replacements

Add rules for finding places where str_plural() can be used. This
currently finds:
 54 files changed, 62 insertions(+), 61 deletions(-)

Co-developed-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Link: https://lore.kernel.org/all/fc1b25a8-6381-47c2-831c-ab6b8201a82b@intel.com/
Signed-off-by: Kees Cook <keescook@chromium.org>

MAINTAINERS

@@ -8979,6 +8979,7 @@ F:	lib/string.c
 F:	lib/string_helpers.c
 F:	lib/test-string_helpers.c
 F:	lib/test_string.c
+F:	scripts/coccinelle/api/string_choices.cocci
 
 GENERIC UIO DRIVER FOR PCI DEVICES
 M:	"Michael S. Tsirkin" <mst@redhat.com>

scripts/coccinelle/api/string_choices.cocci

@@ -0,0 +1,41 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/// Find places to use string_choices.h's various helpers.
+//
+// Confidence: Medium
+// Options: --no-includes --include-headers
+virtual patch
+virtual context
+virtual report
+
+@str_plural depends on patch@
+expression E;
+@@
+(
+-	((E == 1) ? "" : "s")
++	str_plural(E)
+|
+-	((E != 1) ? "s" : "")
++	str_plural(E)
+|
+-	((E > 1) ? "s" : "")
++	str_plural(E)
+)
+
+@str_plural_r depends on !patch exists@
+expression E;
+position P;
+@@
+(
+*	((E@P == 1) ? "" : "s")
+|
+*	((E@P != 1) ? "s" : "")
+|
+*	((E@P > 1) ? "s" : "")
+)
+
+@script:python depends on report@
+p << str_plural_r.P;
+e << str_plural_r.E;
+@@
+
+coccilib.report.print_report(p[0], "opportunity for str_plural(%s)" % e)