radeonsi: extract TXQ buffer size computation into its own function
radeonsi: extract TXQ buffer size computation into its own function

This will allow it to be reused for RESQ.

Reviewed-by: Marek Olšák <8c7344a1abdb103e79ecfd488098373070c3c70e@amd.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler