m68k/atari: Remove obsolete IRQ_TYPE_*

IRQ_TYPE_SLOW, IRQ_TYPE_FAST, and IRQ_TYPE_PRIO are no longer used by
the Atari platform interrupt code since commit 73408565
("[PATCH] m68k: convert atari irq code") in v2.6.18-rc1, so drop them.

Note that their values have been reused for different purposes
(IRQ_TYPE_NONE, IRQ_TYPE_EDGE_RISING, and IRQ_TYPE_EDGE_FALLING) since
commit 6a6de9ef ("[PATCH] genirq: core") in v2.6.18-rc1.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>