We have a use case for checking the results of a DT_PROP_HAS_IDX()
call with COND_CODE_1(). That won't work because its expansion is an
integer comparison; COND_CODE_1() expects a literal 1 or 0.
Adjust the macro implementation so it expands to a literal 1 or 0.
Make this work even when the index argument needs an expansion while
we're at it.
Fixes: #29833
Signed-off-by: Martí Bolívar <marti.bolivar@nordicsemi.no>
ffc03124c1