irqchip/sifive-plic: Chain to parent IRQ after handlers are ready

Now that the PLIC uses a platform driver, the driver is probed later in the
boot process, where interrupts from peripherals might already be pending.

As a result, plic_handle_irq() may be called as early as the call to
irq_set_chained_handler() completes. But this call happens before the
per-context handler is completely set up, so there is a window where
plic_handle_irq() can see incomplete per-context state and crash.

Avoid this by delaying the call to irq_set_chained_handler() until all
handlers from all PLICs are initialized.

Fixes: 8ec99b033147 ("irqchip/sifive-plic: Convert PLIC driver into a platform driver")
Reported-by: Geert Uytterhoeven <[email protected]>
Signed-off-by: Samuel Holland <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Tested-by: Geert Uytterhoeven <[email protected]>
Reviewed-by: Anup Patel <[email protected]>
Cc: [email protected]
Link: https://lore.kernel.org/r/[email protected]
Closes: https://lore.kernel.org/r/CAMuHMdVYFFR7K5SbHBLY-JHhb7YpgGMS_hnRWm8H0KD-wBo+4A@mail.gmail.com/

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