panvk: Fix SampleMask writes for v10+
What does this MR do and why?
Writes to SampleMask were not observed, as the fs.multisampled sysval was not set for v10+.
This fixes some tests in the dEQP-VK.renderpass.suballocation.multisample_resolve.*
, exposing some of the flaky results we have in this suite.
I'm inclined to hold off on merging this until the flakiness has been resolved.