linker: Add Z_LINK_ITERABLE_SUBALIGN

The macro Z_LINK_ITERABLE_SUBALIGN is used by linker scripts to
select the default subalignment based on whether it is 32/64-bit
architecture. 64-bit architectures set the default subalignment
to 8, while 32-bit architectures set it to 4.

Signed-off-by: Peter Mitsis <peter.mitsis@intel.com>
8 files changed