stand: Create MOD_ALIGN macro and use it everywhere

To further reduce the differences between the different MOD_xxx macros,
use MOD_ALIGN to do the proper alignment for the given use.

Sponsored by: Netflix
Differential Revision: https://reviews.freebsd.org/D36570

(cherry picked from commit 8b19d28d68a396b0263e3c13a559a31f70eb3b1d)