x86/pv: Defer I/O bitmap checks even in 64bit mode for emulate_privilege_op()

x86/pv: Defer I/O bitmap checks even in 64bit mode for emulate_privilege_op()

The I/O bitmap doesn't change function depending on mode.  64bit userspace
such as an X server still needs to enter guest_io_okay() to find that the PV
kernel did set up an appropriate virtual I/O bitmap to permit access.

While moving the check, alter its representation to be easier to read.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>