vulkan: Use u_cnd_monotonic for vk_sync_timeline_wait_locked

I was writing some code that waits for an absolute deadline and noticed that cnd_monotonic.h had no users in the code base. This class was added in !7138 (merged) but then the RADV code was deleted in favor of the common Vulkan code, but the common Vulkan code used hacks to deal with C API being CLOCK_REALTIME, instead of using platform APIs that uses CLOCK_MONOTONIC which better suits the purpose.

We should port vk_sync_timeline_wait_locked to u_cnd_monotonic.