regmap: Use select .. if to get IRQ_DOMAIN enabled

Ensure that we can't get randconfig breakage by doing the IRQ_DOMAIN
select automatically. Don't just do the select from REGMAP_IRQ to ensure
that the select actually gets noticed.

Reported-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>