ramips: add D-Link DIR-620 A1 support

Full functionality runtime tested, installation via OEM web-interface requires
a follow-up patch.

Thanks go to Sergey Vasilyugin for his patch that pointed me at the missing
bits (including the antiparallel wps led).

Signed-off-by: Paul Fertser <fercerpav@gmail.com>

SVN-Revision: 33142

target/linux/ramips/base-files/lib/upgrade/platform.sh

@@ -21,6 +21,7 @@ platform_check_image() {
 	dir-300-b1 | \
 	dir-600-b1 | \
 	dir-600-b2 | \
+	dir-620-a1 | \
 	dap-1350 | \
 	esr-9753 | \
 	fonera20n | \