ath79-generic: (re)add Archer C7 v4 (#2497)

Gone due to
commit 45c84a11 ("ar71xx: drop target")

docs/user/supported_devices.rst

@@ -82,7 +82,7 @@ ath79-generic
   - Archer A7 (v5)
   - Archer C5 (v1)
   - Archer C6 (v2)
-  - Archer C7 (v2, v5)
+  - Archer C7 (v2, v4, v5)
   - Archer C59 (v1)
   - CPE210 (v1.0, v1.1, v2.0)
   - CPE220 (v3.0)

targets/ath79-generic

@@ -319,6 +319,10 @@ device('tp-link-archer-c7-v2', 'tplink_archer-c7-v2', {
 	packages = ATH10K_PACKAGES_QCA9880,
 })
 
+device('tp-link-archer-c7-v4', 'tplink_archer-c7-v4', {
+	packages = ATH10K_PACKAGES_QCA9880,
+})
+
 device('tp-link-archer-c7-v5', 'tplink_archer-c7-v5', {
 	packages = ATH10K_PACKAGES_QCA9880,
 })