powerpc/pseries: put cede MSR[EE] check under IRQ_SOFT_MASK_DEBUG

This check does not catch IRQ soft mask bugs, but this option is
slightly more suitable than TRACE_IRQFLAGS.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>