randr12: don't change virtualX/virtualY

randr12: don't change virtualX/virtualY

all the things in the ddx that use virtual* (setting displayWidth, allocating
the FB, EXA init etc) use the values present before this function is called

these prior values are derived from any Virtual line in xorg.conf and are what
we want to use

setting virtual* to the crtc size here, rather than the desired Virtual size,
breaks everything using them in ScreenInit on server regeneration

as the rhd guys say:
	/* This is strange... if we set virtualX/virtualY like the intel driver
	 * does, we limit ourself in the future to this maximum size.
	 * The check for this is internally in RandR, no idea why the intel driver
	 * actually works this way...
	 * Even more curious: if we DON'T update virtual, everything seems to
	 * work as expected... */
so I'll take that as precedent.