irqdomain: Use a dedicated function to set the domain name

The interrupt domain name computation and setting is directly done in
__irq_domain_create(). This leads to a quite long __irq_domain_create()
function.

In order to simplify __irq_domain_create() and isolate the domain name
computation and setting, move the related operations to a dedicated
function.

Signed-off-by: Herve Codina <herve.codina@bootlin.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20240614173232.1184015-6-herve.codina@bootlin.com