system: Add A20 OLinuXino MICRO installer.

* gnu/bootloader/u-boot.scm (u-boot-a20-olinuxino-micro-bootloader): New
exported variable.
* gnu/packages/bootloaders.scm (u-boot-a20-olinuxino-micro): New exported
variable.
* gnu/system/install.scm (a20-olinuxino-micro-installation-os): New exported
variable.

gnu/bootloader/u-boot.scm

@@ -29,6 +29,7 @@
   #:use-module (guix utils)
   #:export (u-boot-bootloader
             u-boot-a20-olinuxino-lime2-bootloader
+            u-boot-a20-olinuxino-micro-bootloader
             u-boot-banana-pi-m2-ultra-bootloader
             u-boot-beaglebone-black-bootloader))
 
@@ -88,6 +89,11 @@
    (inherit u-boot-allwinner-bootloader)
    (package u-boot-a20-olinuxino-lime2)))
 
+(define u-boot-a20-olinuxino-micro-bootloader
+  (bootloader
+   (inherit u-boot-allwinner-bootloader)
+   (package u-boot-a20-olinuxino-micro)))
+
 (define u-boot-banana-pi-m2-ultra-bootloader
   (bootloader
    (inherit u-boot-allwinner-bootloader)

gnu/packages/bootloaders.scm

@@ -431,6 +431,9 @@ also initializes the boards (RAM etc).")
 (define-public u-boot-a20-olinuxino-lime2
   (make-u-boot-package "A20-OLinuXino-Lime2" "arm-linux-gnueabihf"))
 
+(define-public u-boot-a20-olinuxino-micro
+  (make-u-boot-package "A20-OLinuXino_MICRO" "arm-linux-gnueabihf"))
+
 (define-public vboot-utils
   (package
     (name "vboot-utils")

gnu/system/install.scm

@@ -45,6 +45,7 @@
   #:use-module (srfi srfi-26)
   #:export (installation-os
             a20-olinuxino-lime2-emmc-installation-os
+            a20-olinuxino-micro-installation-os
             banana-pi-m2-ultra-installation-os
             beaglebone-black-installation-os))
 
@@ -417,6 +418,22 @@ You have been warned.  Thanks for being so brave.\x1b[0m
                        (tty "ttyS0"))))
                (operating-system-user-services installation-os)))))
 
+(define a20-olinuxino-micro-installation-os
+  (operating-system
+    (inherit installation-os)
+    (bootloader (bootloader-configuration
+                 (bootloader u-boot-a20-olinuxino-lime2-bootloader)
+                 (target "/dev/mmcblk0"))) ; SD card storage
+    (kernel linux-libre)
+    (services (append
+               (list (agetty-service
+                      (agetty-configuration
+                       (extra-options '("-L"))
+                       (baud-rate "115200")
+                       (term "vt100")
+                       (tty "ttyS0"))))
+               (operating-system-user-services installation-os)))))
+
 (define banana-pi-m2-ultra-installation-os
   (operating-system
     (inherit installation-os)