intel/fs: disable VRS when omask is written

intel/fs: disable VRS when omask is written

As indicated by
VkPhysicalDeviceFragmentShadingRatePropertiesKHR::fragmentShadingRateWithShaderSampleMask
our implementation will clamp to 1x1 when reading samplemask or
writing to samplemask.

This fixes vkd3d-proton tests test_sample_mask_dxbc & test_sample_mask_dxil

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Fixes: b6332fc4a8ae58 ("intel/compiler: handle coarse pixel in render target writes descriptors")
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/14553>