Revert raidz_map and _col structure types

As part of the refactoring of ab9f4b0b824ab4cc64a4fa382c037f4154de12d6,
several uint64_t-s and uint8_t-s were changed to other types. This
caused ZoL github issue #6981, an overflow of a size_t on a 32-bit ARM
machine. In absense of any strong motivation for the type changes, this
simply puts them back, modulo the changes accumulated for ABD.

Compile-tested on amd64 and run-tested on armhf.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Gvozden Neskovic <neskovic@gmail.com>
Signed-off-by: Nathaniel Wesley Filardo <nwf@cs.jhu.edu>
Closes #6981
Closes #7023