egl/wayland: Ignore server modifiers for render buffer with PRIME copy
If fd_render_gpu != fd_display_gpu, the buffer allocated here is never sent to the server, and is just copied to a linear buffer. So there is no reason to consider what modifiers the server supports here.
This fixes an issue I see rendering with Nouveau as the DRI_PRIME
render GPU, with a compositor that doesn't advertise "Invalid"
modifiers. I believe it attempted to use a linear buffer (the only
option other than vendor specific modifiers it couldn't use), then
Nouveau failed to render to the buffer with dmesg errors, and just
presented uninitialized memory.
Fixes #8777, which seems to be the same issue I saw. Though I've only tested with Smithay and don't know what dmabuf formats KWin advertises.