gpio: eic-sprd: use raw_spinlock_t in the irq startup path

Summary

In the Linux kernel, the following vulnerability has been resolved: gpio: eic-sprd: use raw_spinlock_t in the irq startup path sprd_eic_irq_unmask() enables the GPIO IRQ and then updates controller state through sprd_eic_update(), which takes sprd_eic->lock with spin_lock_irqsave(). The callback can be reached from irq_startup() while setting up a requested IRQ. That path is not sleepable, but on PREEMPT_RT a regular spinlock_t becomes a sleeping lock. This issue was found by our static analysis tool and then manually reviewed against the current tree. The grounded PoC kept the request_threaded_irq() -> __setup_irq() -> irq_startup() -> sprd_eic_irq_unmask() -> sprd_eic_update() carrier and used the original spin_lock_irqsave(&sprd_eic->lock) edge. Lockdep BUG: sleeping function called from invalid context hardirqs last disabled at ... __setup_irq.constprop.0 ... [vuln_msv] sprd_rt_spin_lock_irqsave+0x1c/0x30 [vuln_msv] sprd_eic_update.constprop.0+0x48/0x90 [vuln_msv] sprd_eic_irq_unmask.constprop.0+0x35/0x50 [vuln_msv] __setup_irq.constprop.0+0xd/0x30 [vuln_msv] Convert the Spreadtrum EIC controller lock to raw_spinlock_t. The locked section only serializes MMIO register updates and does not contain sleepable operations, so keeping it non-sleeping is appropriate for the irqchip callbacks.