sandbox: rename dummy 'host' device to 'hostfs' to reflect it's usage

This renames the dummy 'host' device to hostfs to better reflect it's
usage and make room for using 'host' for actual host block device driver.
sandbox: block driver using host file/device as backing store

A simple "host" block driver using any host file/device
as backing store.

Adds two sb subcommands for managing host device bindings:
sb bind <dev> [<filename>] - bind "host" device to file
sb info [<dev>]            - show device binding & info

Signed-off-by: Henrik Nordstrom <henrik@henriknordstrom.net>

Series-to: uboot
Series-cc: Simon Glass <sjg@chromium.org>
Series-version: 3

Series-changes: 3
- blank line between declarations and code
- declarations at top
- rename sandboxblockdev.h to sandbox-blockdev.h
- correct ordering in drivers/block/Makefile
- errno return from host_dev_bind (was command return)
- puts instead of printf where applicable
- documented "sb bind" and "sb info" commands in SANDBOX.readme

Series-changes: 2
- add "sb info" command for querying current bound devices
- make filename optional to "sb bind". Unbinds if not given
- verify argument correctness in "sb bind"
- add HOST device type name for part list
- make "sb bind" immediately attach the device instead of on first use
- enable EFI/GUID partitions as in sandbox config

Todo:
- Documentation
- Testsuite

sandbox: Restore sanbox virtual 'host' device dummy

Document sb bind and sb info commands a bit
sandbox: Enable generic fs commands (load/save/ls etc)