intel: Refactor quantize_num_samples

intel: Refactor quantize_num_samples

Rename quantize_num_samples to intel_quantize_num_samples and change the
first param from struct intel_context* to struct intel_screen*. The
function will later be used by intelCreateBuffer, which is not bound to
any context but is bound to a screen.

Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Paul Berry <stereotype441@gmail.com> (v1)
Signed-off-by: Chad Versace <chad.versace@linux.intel.com>