powerpc/kuap: PPC_KUAP_DEBUG should depend on PPC_KUAP

powerpc/kuap: PPC_KUAP_DEBUG should depend on PPC_KUAP

Currently you can enable PPC_KUAP_DEBUG when PPC_KUAP is disabled,
even though the former has not effect without the latter.

Fix it so that PPC_KUAP_DEBUG can only be enabled when PPC_KUAP is
enabled, not when the platform could support KUAP (PPC_HAVE_KUAP).

Fixes: 890274c2dc4c ("powerpc/64s: Implement KUAP for Radix MMU")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200301111738.22497-1-mpe@ellerman.id.au