drm/imagination: Mask GPU IRQs in threaded handler

drm/imagination: Mask GPU IRQs in threaded handler

Pass IRQF_ONESHOT flag to request_threaded_irq(), so that interrupts will
be masked by the kernel until the end of the threaded IRQ handler. Since
the calls to pvr_fw_irq_enable() and pvr_fw_irq_disable() are now
redundant, remove them.

Interrupts to the host from the soon-to-be-added RISC-V firmware
processors cannot be masked in hardware. This change allows us to continue
using the threaded handler in GPUs with a RISC-V firmware.

For simplicity, the same approach is taken for all firmware processors.

Signed-off-by: Alessio Belle <alessio.belle@imgtec.com>
Reviewed-by: Frank Binns <frank.binns@imgtec.com>
Link: https://lore.kernel.org/r/20250410-sets-bxs-4-64-patch-v1-v6-6-eda620c5865f@imgtec.com
Signed-off-by: Matt Coster <matt.coster@imgtec.com>