cs5535: CS5535_MFGPT_DEFAULT_IRQ should depend on CS5535_MFGPT

It doesn't make much sense to have CS5535_MFGPT_DEFAULT_IRQ show up in
configs that cannot have CS5535_MFGPT.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Andres Salomon <dilinger@collabora.co.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>