nir: Use BITSET for tracking varyings in lower_io_arrays

nir: Use BITSET for tracking varyings in lower_io_arrays

MAX_VARYINGS_INCL_PATCH is greater than 64, so we'll need more that 64
bits (per component) to track which vars have indirects. This pass was
trying to track patch varyings (which start at bit 63) in a separate
64 bit word, but failed to subtract VARYING_SLOT_PATCH0 and accessed
out of bounds.

Do away with the ad-hoc bit mask tracking and just use a BITSET.

Fixes: dEQP-GLES31.functional.tessellation.user_defined_io.per_patch_block.vertex_io_array_size_implicit.triangles
Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>
Signed-off-by: Kristian H. Kristensen <hoegsberg@google.com>