isl: Refactor row pitch calculation (v2)

isl: Refactor row pitch calculation (v2)

The calculations of row_pitch, the row pitch's alignment, surface size,
and base_alignment were mixed together. This patch moves the calculation
of row_pitch and its alignment to occur before the calculation of
surface_size and base_alignment.

This simplifies a follow-on patch that adds a new member, 'row_pitch',
to struct isl_surf_init_info.

v2:
  - Also extract the row pitch alignment.
  - More helper functions that will later help validate the row pitch.

Reviewed-by: Nanley Chery <nanley.g.chery@intel.com> (v2)
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net> (v2)