gnu: u-boot-nintendo-nes-classic-edition: Make it actually boot again.

* gnu/packages/patches/u-boot-nintendo-nes-serial.patch: New file.
* gnu/local.mk (dist_patch_DATA): Add u-boot-nintendo-nes-serial.patch.
* gnu/packages/bootloaders.scm (u-boot-nintendo-nes-classic-edition): Downgrade to 2018.11.
[source]: Add patch.
[description]: Modify.
[native-inputs]: Add python-2.

gnu/packages/bootloaders.scm

@@ -802,7 +802,34 @@ it fits within common partitioning schemes.")
   (make-u-boot-package "A20-OLinuXino_MICRO" "arm-linux-gnueabihf"))
 
 (define-public u-boot-nintendo-nes-classic-edition
-  (make-u-boot-package "Nintendo_NES_Classic_Edition" "arm-linux-gnueabihf"))
+  (let ((base (make-u-boot-package "Nintendo_NES_Classic_Edition"
+                                   "arm-linux-gnueabihf")))
+    (package
+      (inherit base)
+      ;; Starting with 2019.01, FEL doesn't work anymore on A33.
+      (version "2018.11")
+      (source (origin
+                (method url-fetch)
+                (uri (string-append
+                      "https://ftp.denx.de/pub/u-boot/"
+                      "u-boot-" version ".tar.bz2"))
+                (sha256
+                 (base32
+                  "0znkwljfwwn4y7j20pzz4ilqw8znphrfxns0x1lwdzh3xbr96z3k"))
+                (patches (search-patches
+                           "u-boot-nintendo-nes-serial.patch"))))
+      (description "U-Boot is a bootloader used mostly for ARM boards.  It
+also initializes the boards (RAM etc).
+
+This version is for the Nintendo NES Classic Edition.  It is assumed that
+you have added a serial port to pins PB0 and PB1 as described on
+@url{https://linux-sunxi.org/Nintendo_NES_Classic_Edition}.
+
+In order to use FEL mode on the device, hold the Reset button on the
+device while it's being turned on (and a while longer).")
+      (native-inputs
+       `(("python" ,python-2)
+         ,@(package-native-inputs base))))))
 
 (define-public u-boot-wandboard
   (make-u-boot-package "wandboard" "arm-linux-gnueabihf"))