ccid: add passthru card device

The passthru ccid card is a device sitting on the usb-ccid bus and
using a chardevice to communicate with a remote device using the
VSCard protocol defined in libcacard/vscard_common.h

Usage docs available in following patch in docs/ccid.txt

Signed-off-by: Alon Levy <alevy@redhat.com>

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Changes from v23->v24:
 * fixed double license line in header.

Changes from v20->v21: (Jes Sorensen review)
 * add reference to COPYING in header
 * long comment reformatting

Changes from v19->v20:
 * checkpatch.pl

Changes from v18->v19:
 * add qdev.desc
 * remove .qdev.unplug (no hot unplug support for ccid bus)

Changes from v16->v17:
 * fix wrong cast when receiving VSC_Error
 * ccid-card-passthru: force chardev user wakeup by sending Init
   see lengthy comment below.

Changes from v15->v16:

Behavioral changes:
 * return correct size
 * return error instead of assert if client sent too large ATR
 * don't assert if client sent too large a size, but add asserts for indices to buffer
 * reset vscard_in indices on chardev disconnect
 * handle init from client
 * error if no chardev supplied
 * use ntoh, hton
 * eradicate reader_id_t
 * remove Reconnect usage (removed from VSCARD protocol)
 * send VSC_SUCCESS on card insert/remove and reader add/remove

Style fixes:
 * width of line fix
 * update copyright
 * remove old TODO's
 * update file header comment
 * use macros for debug levels
 * c++ style comment replacement
 * update copyright license
 * fix ATR size comment
 * fix whitespace in struct def
 * fix DPRINTF prefix
 * line width fix

ccid-card-passthru: force chardev user wakeup by sending Init

The problem: how to wakeup the user of the smartcard when the smartcard
device is initialized?

Long term solution: have a callback interface. This was done via
the deprecated so called chardev ioctl interface.

Short term solution: do a write. Specifically we write an Init message.
And we change the client to send it's own Init message regardless of
receiving this one. Additional Init messages will be regarded as
acceptable, the first one received after connection establishment is
the determining one wrt capabilities.
