lib: move 64-bit div/mod compiler helpers

lib: move 64-bit div/mod compiler helpers

These were built for 32-bit architectures only (the same code could,
with some tweaking, sensibly be used to provide TI-mode helpers on
64-bit arch-es) - retain this property, while still avoiding to have
a CU without any contents at all. For this, Arm's CONFIG_64BIT gets
generalized.

Note that we imply "32-bit arch" to be the same as BITS_PER_LONG == 32,
i.e. we aren't (not just here) prepared to have a 64-bit arch with
BITS_PER_LONG == 32. Yet even if we supported such, likely the compiler
would get away there without invoking these helpers, so the code would
remain unused in practice.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Julien Grall <jgrall@amazon.com>