gallium/util: Add u_bit_scan_consecutive_range64.
gallium/util: Add u_bit_scan_consecutive_range64.

For use by radeonsi.

v2: Make sure that it works for all 64 bits set.

Signed-off-by: Bas Nieuwenhuizen <1d31d94f30d40df7951505d1034e1e923d02ec49@basnieuwenhuizen.nl>
Reviewed-by: Marek Olšák <8c7344a1abdb103e79ecfd488098373070c3c70e@amd.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler