slw: Fix indication of whether sleep is supported
slw: Fix indication of whether sleep is supported

Don't enable it if HB doesn't allow it and fix backward logic in
the code that was supposed to disable it. Also print out more
diagnostic info.

Signed-off-by: Benjamin Herrenschmidt <a7089bb6e7e92505d88aaff006cbdd60cc9120b6@kernel.crashing.org>

neelegup/skiboot,cyrilbur-ibm/skiboot,csmart/skiboot,open-power/skiboot,csmart/skiboot,qemu/skiboot,ddstreet/skiboot,ddstreet/skiboot,shenki/skiboot,stewart-ibm/skiboot,apopple/skiboot,legoater/skiboot,neelegup/skiboot,shenki/skiboot,open-power/skiboot,shenki/skiboot,mikey/skiboot,apopple/skiboot,stewart-ibm/skiboot,csmart/skiboot,shenki/skiboot,jk-ozlabs/skiboot,jk-ozlabs/skiboot,legoater/skiboot,qemu/skiboot,legoater/skiboot,open-power/skiboot,apopple/skiboot,neelegup/skiboot,legoater/skiboot,qemu/skiboot,cyrilbur-ibm/skiboot,legoater/skiboot,ddstreet/skiboot,open-power/skiboot,open-power/skiboot,mikey/skiboot,cyrilbur-ibm/skiboot,mikey/skiboot,shenki/skiboot,stewart-ibm/skiboot,qemu/skiboot,jk-ozlabs/skiboot,qemu/skiboot