genirq: Make handle_enforce_irqctx() unconditionally available

Commit 1b57d91b ("irqchip/gic-v2, v3: Prevent SW resends entirely")
sett the flag which enforces interrupt handling in interrupt context and
prevents software base resends for ARM GIC v2/v3.

But it missed that the helper function which checks the flag was hidden
behind CONFIG_GENERIC_PENDING_IRQ, which is not set by ARM[64].

Make the helper unconditionally available so that the enforcement actually
works.

Fixes: 1b57d91b ("irqchip/gic-v2, v3: Prevent SW resends entirely")
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20241210101811.497716609@linutronix.de