ARM: uniphier: add emmcupdate command

The Boot ROM expects the boot image (SPL) in the Boot Partition 1.
So, updating images involves the hardware partition switch.  It might
be a bit advanced for some users.

To be user-friendly, this commit adds a useful command to update the
images; just put SPL and U-Boot proper into the public directory of
the TFTP server and execute "run emmcupdate" from the command line.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
diff --git a/doc/README.uniphier b/doc/README.uniphier
index c270ecb..5ac52bd 100644
--- a/doc/README.uniphier
+++ b/doc/README.uniphier
@@ -78,6 +78,20 @@
   => run nandupdate
 
 
+Burn U-Boot images to eMMC
+--------------------------
+
+Write two files to the Boot partition 1 of the eMMC device as follows:
+ - spl/u-boot-spl.bin at the offset address 0x00000000
+ - u-boot.img         at the offset address 0x00010000
+
+If a TFTP server is available, the images can be easily updated.
+Just copy the u-boot-spl-dtb.bin and u-boot-dtb.img to the TFTP public
+directory, and then run the following command at the U-Boot command line:
+
+  => run emmcupdate
+
+
 UniPhier specific commands
 --------------------------