resource: add define macro for register address resources

DEFINE_RES_ macros have been created for the commonly used resource types,
but not IORESOURCE_REG. Add the macro so it can be used in a similar manner
to all other resource types.

Signed-off-by: Colin Foster <colin.foster@in-advantage.com>
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20220905162132.2943088-7-colin.foster@in-advantage.com