[XSM][FLASK] Argument handling bugs in XSM:FLASK

[XSM][FLASK] Argument handling bugs in XSM:FLASK

Addresses a number of argument handling bugs in the flask_op hypercall
in the XSM:Flask module.  Thanks to Rafal Wojtczuk at McAfee for
reporting the issues and Tim Deegan at Citrix for providing an
initial patch.

This patch addresses the following issues:
 - bounds checking and validation on input arguments to flask_op
 - updated ABI/API, size and cmd are now uint32_t
 - updated userspace tools and libraries to account for ABI/API
 changes
 - implemented all copies using from/to guest, better portability
 - implemented upper bounds checking on op->cmd, op->size
 - implemented sanity checking on op->size and op->buf
 - implemented bit vector for checking from/to usage on op->cmd

Signed-off-by: George Coker <gscoker@alpha.ncsc.mil>