aco: Optimize out s_and with exec, when used on uniform bitwise values.

aco: Optimize out s_and with exec, when used on uniform bitwise values.

Previously all booleans needed an s_and with exec when they were turned
into a scalar condition. However, this is not needed for uniform booleans.

v2 by Daniel Schürmann:
- Make the code more readable
v3 by Timur Kristóf:
- Fix regressions, make it work in wave32 mode

Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
Reviewed-by: Daniel Schürmann <daniel@schuermann.dev>