venus: defer bo allocation for direct alloc of non-external memory until vn_MapMemory
The bo is only needed when we want to setup driver side mapping for the device memory. By deferring the bo allocation, we avoid holding extra open fds exported via get_blob at allocation time. This works around small RLIMIT_NOFILE
for some processes to pass cts.
For more context, please check virgl/virglrenderer!648 (comment 1161351)
Test:
dEQP-VK.memory.*
dEQP-VK.api.*
Edited by Yiwei Zhang