Uboot bootstate (#215)

* Uboot: cleaning up bootstate env import/export.

* Tinker: Add potential eMMC boot support.

buildroot-external/board/raspberrypi/rpi3-64/uboot-boot.sh

@@ -1,3 +1,17 @@
+
+part start mmc ${devnum} 6 mmc_env
+mmc dev ${devnum}
+setenv loadbootstate " \
+    echo 'loading env...'; \
+    mmc read ${ramdisk_addr_r} ${mmc_env} 0x20; \
+    env import -c ${ramdisk_addr_r} 0x4000;"
+
+setenv storebootstate " \
+    echo 'storing env...'; \
+    env export -c -s 0x4000 ${ramdisk_addr_r} BOOT_ORDER BOOT_A_LEFT BOOT_B_LEFT; \
+    mmc write ${ramdisk_addr_r} ${mmc_env} 0x20;"
+
+run loadbootstate
 test -n "${BOOT_ORDER}" || setenv BOOT_ORDER "A B"
 test -n "${BOOT_A_LEFT}" || setenv BOOT_A_LEFT 3
 test -n "${BOOT_B_LEFT}" || setenv BOOT_B_LEFT 3
@@ -38,12 +52,12 @@ done
 
 setenv fdt_addr
 if test -n "${bootargs}"; then
-  saveenv
+  run storebootstate
 else
   echo "No valid slot found, resetting tries to 3"
   setenv BOOT_A_LEFT 3
   setenv BOOT_B_LEFT 3
-  saveenv
+  run storebootstate
   reset
 fi