i965: Use genxml for emitting PIPE_CONTROL.

i965: Use genxml for emitting PIPE_CONTROL.

While this does add a bunch of boilerplate, it also protects us against
the hardware moving bits, or changing their meaning.  For something as
finnicky as PIPE_CONTROL, the extra safety seems worth it.

We turn PIPE_CONTROL_* into an bitfield of arbitrary flags, and then
pack them appropriately.

Reviewed-by: Topi Pohjolainen <topi.pohjolainen@intel.com>