Add a new set of helpers for expanding property entries with a
separator. These macros complement DT(_INST)FOREACH_PROP_ELEM(_VARGS) by
adding the capability to expand with a custom separator between property
entries. This allows, in some cases, to re-use existing macros (e.g.
DT_PROP_BY_IDX) without creating an auxiliary macro that just appends a
separator. Example:
```dts
n: node {
...
my-gpios = <&gpioa 0 GPIO_ACTIVE_HIGH>,
<&gpiob 1 GPIO_ACTIVE_HIGH>;
};
```
Before:
```c
#define GPIO_DT_SPEC_BY_IDX_AND_COMMA(node_id, prop, idx) \
GPIO_DT_SPEC_BY_IDX(node_id, prop, idx),
struct gpio_dt_spec specs[] = {
DT_FOREACH_PROP_ELEM(DT_NODELABEL(n), my_gpios,
GPIO_DT_SPEC_BY_IDX_AND_COMMA)
};
```
After:
```c
struct gpio_dt_spec specs[] = {
DT_FOREACH_PROP_ELEM_SEP(DT_NODELABEL(n), my_gpios,
GPIO_DT_SPEC_BY_IDX, (,))
};
```
Signed-off-by: Gerard Marull-Paretas <gerard.marull@nordicsemi.no>
fdea3c9a44