gpio: ml-ioh: use raw_spinlock_t for the register lock

In the Linux kernel, the following vulnerability has been resolved: gpio: ml-ioh: use raw_spinlock_t for the register lock ioh_irq_type() is registered as the irq_chip .irq_set_type callback and takes chip->spinlock with spin_lock_irqsave(). This callback is reached from __setup_irq() -> __irq_set_trigger() -> chip->irq_set_type() while the caller holds desc->lock, a raw_spinlock_t, with hardirqs disabled. That context is not sleepable, but on PREEMPT_RT a regular spinlock_t is an rtmutex-backed sleeping lock, so acquiring it there is invalid. ioh_irq_enable() and ioh_irq_disable() take the same lock from the .irq_enable/.irq_disable callbacks, which are likewise invoked with desc->lock held. Convert the register lock to raw_spinlock_t. The same lock also serializes the GPIO direction/value callbacks and the suspend/resume register save/restore, and those critical sections only perform short sequences of MMIO register accesses (ioread32()/iowrite32()); the .irq_set_type callback additionally emits a dev_warn() on an unsupported type. None of these are sleepable operations, so keeping this register lock non-sleeping is appropriate for the irqchip callbacks and does not change the GPIO-side locking contract. This is the same fix as commit a02b8950d619 ("gpio: pch: use raw_spinlock_t for the register lock"); this driver shares the same structure as gpio-pch.

Quoted source text, attributed separately from HOL analysis.