virgl: add extra checks in virgl_res_needs_flush_wait

virgl: add extra checks in virgl_res_needs_flush_wait

This is motivated by the following scenario:

glSubBufferData(GL_ARRAY_BUFFER, ...)
glFlush(..)
glSubBufferData(GL_ARRAY_BUFFER, ...)
glSubBufferData(GL_ARRAY_BUFFER, ...)
glSubBufferData(GL_ARRAY_BUFFER, ...)

This increases @davidriley's Team Fortress 2 apitrace from
1 fps to 6 fps and helps with the Chromium glbench
microbenchmarks:

Before: texture_update_rgba_texsubimage2d_2048 = 554.96 mtexel_sec
   buffer_upload_dynamic_array_12 = 0.02 mbytes_sec
   buffer_upload_dynamic_array_576 = 1.07 mbytes_sec
After: texture_update_rgba_texsubimage2d_2048 = 612.29 mtexel_sec
   buffer_upload_dynamic_array_12 = 2.22 mbytes_sec
   buffer_upload_dynamic_array_576 = 164.89 mbytes_sec
Reviewed-by: Gert Wollny <gert.wollny@collabora.com>