fastboot: check for alias when looking up partition by name

Implement an alias name check for devices where GPT limitations prevent
user-friendly partition names such as "boot", "system" and "cache". Or,
where the actual partition name doesn't match a standard partition name
used commonly with fastboot.

To set an alias, add an environment setting as follows:
fastboot_partition_alias_<alias partition name>=<actual partition name>

Example: fastboot_partition_alias_boot=LNX

Signed-off-by: Michael Scott <michael.scott@linaro.org>
Acked-by: Steve Rae <srae@broadcom.com>
Cc: Steve Rae <srae@broadcom.com>
Cc: Lukasz Majewski <l.majewski@samsung.com>
diff --git a/doc/README.android-fastboot b/doc/README.android-fastboot
index 5526a43..04411e9 100644
--- a/doc/README.android-fastboot
+++ b/doc/README.android-fastboot
@@ -50,6 +50,15 @@
 buffer and size are set with CONFIG_USB_FASTBOOT_BUF_ADDR and
 CONFIG_USB_FASTBOOT_BUF_SIZE.
 
+Fastboot partition aliases can also be defined for devices where GPT
+limitations prevent user-friendly partition names such as "boot", "system"
+and "cache".  Or, where the actual partition name doesn't match a standard
+partition name used commonly with fastboot.  Current implentation checks
+aliases when accessing partitions by name (flash_write and erase functions).
+To define a partition alias add an environment variable similar to:
+fastboot_partition_alias_<alias partition name>=<actual partition name>
+Example: fastboot_partition_alias_boot=LNX
+
 In Action
 =========
 Enter into fastboot by executing the fastboot command in u-boot and you