anv: Account for dynamic stencil write disables in the PMA fix

In 6ce85928 we started looking at the dynamic stencil state and
disabling stencil writes when the stencil mask is zero.  Unfortunately,
we never updated the PMA fix code accordingly so 3DSTATE_WM_DEPTH_STENCIL
and the PMA fix were getting out-of-sync causing hangs.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=109203


Fixes: 6ce85928 "anv: Disable stencil writes when both write..."
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
(cherry picked from commit 6a441151)