powerpc: Don't include asm/prom.h in asm/parport.h

parport.h needs only of_irq.h, no need to go via asm/prom.h

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/ec796ee56cf61f16ba24e62a9d3525d11931538c.1646767214.git.christophe.leroy@csgroup.eu