etnaviv/drm: fix size limit in etna_cmd_stream_realloc

The intended limit for command stream size is 64KB, as this is what old kernels can reliably do and what allows for maximum number of queued streams on newer kernels. However, due to unit confusion with the size member, which is in dwords, the submitted streams could grow up to ~128KB. Fix this by using the proper limit in dwords.

Flushing due to some limits being exceeded is not an issue, but is expected with certain workloads, so lower the severity of the message being emitted in this case to debug level.