package/pkg-utils: add 'provides' to show-info

Add the list of virtual packages a show-info entry provides to the
output.

For more information on virtual packages infrastructure see [1]

[1] https://buildroot.org/downloads/manual/manual.html#_infrastructure_for_virtual_packages

Signed-off-by: Thomas Perale <thomas.perale@mind.be>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/pkg-utils.mk

@@ -201,9 +201,16 @@ define _json-info-pkg-details
 		$(foreach patch, \
 			$(call pkg-patches-list,$(1)), \
 			$(call mk-json-str,$(patsubst $(CONFIG_DIR)/%,%,$(patch)))$(comma) \
-
 		)
 	],
+	$(if $($(1)_PROVIDES), \
+		"provides": [ \
+			$(foreach provide, \
+				$($(1)_PROVIDES), \
+				$(call mk-json-str,$(provide))$(comma) \
+			) \
+		]$(comma) \
+	)
 endef
 
 define _json-info-fs