drm/i915: Flatten a bunch of the pfit functions

Most of the pfit functions are of the form:

func()
{
	if (pfit_enabled) {
		...
	}
}

Flip the pfit_enabled check around to flatten the functions.

And while we're touching all this let's do the usual
s/pipe_config/crtc_state/ replacement.
Reviewed-by: Manasi Navare <manasi.d.navare@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200422161917.17389-2-ville.syrjala@linux.intel.com