util/intelp2m: Set GO111MODULE environment parameter explicitly

With go1.16 the default for GO111MODULE changed to on which break
building this tool.

Change-Id: I93a516ff76c8da4b7f37157d58ecd4c0b09c582c
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/52862
Reviewed-by: Jonathan Zhang <jonzhang@fb.com>
Reviewed-by: David Hendricks <david.hendricks@gmail.com>
Reviewed-by: Maxim Polyakov <max.senia.poliak@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

util/intelp2m/Makefile

@@ -5,7 +5,7 @@ PROJECT_NAME = intelp2m
 
 default:
 	go version
-	go build -v -o $(PROJECT_NAME)
+	GO111MODULE=off go build -v -o $(PROJECT_NAME)
 
 clean:
 	rm -Rf $(PROJECT_NAME) $(OUTPUT_DIR)