drm/i915: Make pipe_offsets[] & co. u32

Using a signed type for the register offsets doesn't really
make sense. Switch to u32.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220623130900.26078-5-ville.syrjala@linux.intel.com


Reviewed-by: Jani Nikula <jani.nikula@intel.com>