python: Adjust xc_physinfo wrapper for updated virt_caps bits

python: Adjust xc_physinfo wrapper for updated virt_caps bits

Commit f089fddd94 "xen: report PV capability in sysctl and use it in
toolstack" changed meaning of virt_caps bit 1 - previously it was
"directio", but was changed to "pv" and "directio" was moved to bit 2.
Adjust python wrapper to use #defines for the bits values, and add
reporting of both "pv_directio" and "hvm_directio".

Signed-off-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>