i965: Change fragment input related bitfields to 64-bit.

This patch updates the bitfields brw_context::wm.input_size_masks,
tracker::size_masks, and brw_wm_prog_key::proj_attrib_mask, all of
which are indexed by gl_frag_attrib, from 32-bit to 64-bit.

This paves the way for supporting geometry shaders, and for merging
the gl_frag_attrib and gl_vert_result enums.  The combination of these
two will require at least 55 bits in the bitfields.