nir: add lower_bitshift option

Add a "lower_bitshift" option, which disables optimizations introducing
bitshifts and lowers ishl by constant to a multiply, so that we don't have
to deal with bitshifts in int_to_float lowering.

Signed-off-by: Jonathan Marek <jonathan@marek.ca>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>

src/gallium/drivers/lima/lima_program.c

@@ -50,6 +50,7 @@ static const nir_shader_compiler_options vs_nir_options = {
    .lower_ftrunc = true,
    /* could be implemented by clamp */
    .lower_fsat = true,
+   .lower_bitshift = true,
 };
 
 static const nir_shader_compiler_options fs_nir_options = {