anv: Emit load clears at start of each subpass

This should improve cache residency for render targets.

Pre-patch, vkCmdBeginRenderPass emitted all the meta clears for
VK_ATTACHMENT_LOAD_OP_CLEAR before any subpass began. Post-patch,
vCmdBeginRenderPass and vkCmdNextSubpass emit only the clears needed for
that current subpass.
4 files changed