storage: Streaming interface and block implementation

This patch adds an implementation in depthcharge for the streaming
interface. It updates for catching up bf473e8bd112c428d2e8ccdfd2c6acc8042cd2d6.

BUG=NONE
TEST=Boots to kernel.

Change-Id: I93f2cd76069156064906a063427a689ad3ac5ee1
depthcharge: fix main_fmap content changed bug

The buffer content returned by flash_read should not be changed
afterward because other modules may need it(such as main_fmap).

Change-Id: I9e7e79134d225c033f3fae41f91a6aa93b94cc11