[host] Remove calls to fbl::AutoCall

fbl::AutoCall is deprecated in host/userspace in favor of fit::defer.

Calls to fbl::AutoCall could not be removed from kernel or system code
since they may not have the C++ standard library included.

TEST=runtests
CP-146: #progress

Change-Id: Ief2f908430c17851f9f40e4bbabbe122005033d6

[dev][xdc-server] Process reads from UsbHandler.

Currently just handles ctrl messages - prints when a xdc device stream
goes on or offline.

Adds the UsbHandler::Transfer type which will wrap around a
libusb_transfer.

TEST= with local usb-handler changes patched in
out/build-zircon/tools/xdc-server
fx shell xdc-test -u -f file

Change-Id: I25ac882f79e6629b346a4467579886f54974a0bc

[host][xdc-server] Handle usb handler fd changes.

The usb handler will handle all libusb related activity.

The xdcserver will monitor for events on the usb handler fds.
For now just handle the event where the usb handler adds / removes fds.

The actual usb handler implementation is left to a future CL
once libusb is added to sysroot (BLD-214)

TEST= patched local usb handler changes
out/build-zircon/tools/xdc-server
Unplugged and plugged in debugging cable.

Change-Id: I11e16bde744dad8495f7b299d26ef4859d6ef611

[ulib][xdc-host] Move socket stuff to header file.

This is for a future client app to use to connect to the xdc-server.

TEST= out/build-zircon/tools/xdc-server

Change-Id: I75c701b11dc864f6d18d4e6bf954866f09af9c51

[host][xdcserver] Beginnings of xdc host server.

The xdcserver will sit between host side clients and libusb.

Clients will open a socket to the xdc server and register for a stream
id.

In a future CL, client reads / writes after registering will
be transformed into libusb requests by the xdcserver, which are
then passed on to the xdc server on the device side and routed
to the appropriate stream id.

TEST= out/build-zircon/tools/xdc-server and
run test app added in
https://fuchsia-review.googlesource.com/c/zircon/+/174059

Change-Id: I2420317a209f42b56bf9968fce08eec3ae1ef775