usb: gadget: fastboot: Add fastboot erase

Adds the fastboot erase functionality, to erase a partition
specified by name. The erase is performed based on erase group size,
to avoid erasing other partitions. The start address and the size
is aligned to the erase group size for this.

Currently only supports erasing from eMMC.

Signed-off-by: Dileep Katta <dileep.katta@linaro.org>
Reviewed-by: Lukasz Majewski <l.majewski@samsung.com>
diff --git a/doc/README.android-fastboot b/doc/README.android-fastboot
index 1677609..5526a43 100644
--- a/doc/README.android-fastboot
+++ b/doc/README.android-fastboot
@@ -6,9 +6,8 @@
 The protocol that is used over USB is described in
 README.android-fastboot-protocol in same directory.
 
-The current implementation does not yet support the erase command or the
-"oem format" command, and there is minimal support for the flash command;
-it only supports eMMC devices.
+The current implementation is a minimal support of the erase command,the
+"oem format" command and flash command;it only supports eMMC devices.
 
 Client installation
 ===================