arm: dsputil: Drop restrict keyword from add_pixels_clamped_armv6 prototype

The function is assigned to a function pointer that does not have the
restrict keyword for that parameter.

This fixes compilation for MSVC builds that don't recognize "restrict",
broken since ed9625eb62.
configure: Group and sort function/struct/type checks

Group checks into logical groups and sort alphabetically within those groups
unless checks have close coupling. Keep closely coupled checks together.
configure: Split some logical blocks off from CONFIG_LIST
configure: Split some logical blocks off from HAVE_LIST