genirq/debugfs: Print irqdomain flags as human-readable strings

Improve the readability of irqdomain debugging information in debugfs by
printing the flags field of domain files as human-readable strings instead
of a raw bitmask, which aligned with the existing style used for irqchip
flags in the irq debug files.

Before:
	#cat :cpus:cpu@0:interrupt-controller
	name:   :cpus:cpu@0:interrupt-controller
	 size:   0
	 mapped: 2
	 flags:  0x00000003

After:
	#cat :cpus:cpu@0:interrupt-controller
	name:   :cpus:cpu@0:interrupt-controller
	 size:   0
	 mapped: 3
	 flags:  0x00000003
	            IRQ_DOMAIN_FLAG_HIERARCHY
	            IRQ_DOMAIN_NAME_ALLOCATED

Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20240529091628.3666379-1-ruanjinjie@huawei.com