drm/panfrost: Add gpu_irq, mmu_irq to struct panfrost_device

In preparation for adding a IRQ synchronization mechanism for PM suspend,
add gpu_irq and mmu_irq variables to struct panfrost_device and change
functions panfrost_gpu_init() and panfrost_mmu_init() to use those.

Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231204114215.54575-3-angelogioacchino.delregno@collabora.com