devicetree: reorder instance property macros

Reorder the instance number property access macros. The non-instance
number ones appear in this order: DT_PROP(), DT_PROP_LEN(),
DT_PROP_HAS_IDX(), DT_PROP_BY_IDX(), DT_LABEL().

Improves readability slightly by moving code around so INST versions
appear in the same order as non-INST versions.

No functional changes expected.

Signed-off-by: Martí Bolívar <marti.bolivar@nordicsemi.no>