drm/i915/irq: add struct i915_irq_regs triplet

drm/i915/irq: add struct i915_irq_regs triplet

Add struct i915_irq_regs to hold IMR/IER/IIR register offsets to pass to
gen3_irq_reset() and gen3_irq_init(). This helps in grouping the
registers and further cleanup.

Note: gen3_irq_reset() and gen3_irq_init() really did have the
IMR/IER/IIR parameters in different order.

Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241002102645.136155-1-jani.nikula@intel.com
Signed-off-by: Jani Nikula <jani.nikula@intel.com>