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

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
reported:

  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.

Fixes: 25518e024e3a ("gpio: Add Spreadtrum EIC driver support")
Cc: stable@vger.kernel.org
Signed-off-by: Runyu Xiao <runyu.xiao@seu.edu.cn>
Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://patch.msgid.link/20260617154035.1199948-3-runyu.xiao@seu.edu.cn
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>