anv: Fix VK_EXT_transform_feedback working with varyings packed in PSIZ

anv: Fix VK_EXT_transform_feedback working with varyings packed in PSIZ

Transform feedback did not set correct SO_DECL.ComponentMask for
varyings packed in VARYING_SLOT_PSIZ:
 gl_Layer         - VARYING_SLOT_LAYER    in VARYING_SLOT_PSIZ.y
 gl_ViewportIndex - VARYING_SLOT_VIEWPORT in VARYING_SLOT_PSIZ.z
 gl_PointSize     - VARYING_SLOT_PSIZ     in VARYING_SLOT_PSIZ.w

Fixes: 36ee2fd61c8f94 "anv: Implement the basic form of VK_EXT_transform_feedback"

Signed-off-by: Danylo Piliaiev <danylo.piliaiev@globallogic.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>