external/mambo: Updates POWER9 SIM_CTRL1 to remove hardware atomic RC
external/mambo: Updates POWER9 SIM_CTRL1 to remove hardware atomic RC

Update SIM_CTRL1 bits to set ARC0/1, which disables atomic RC updates in
hardware which matches implementation.

Comment some remaining quirks with the P9 configuration.

Signed-off-by: Nicholas Piggin <24829078df5003d9dd1dd871ca2aeb0b1cf95ef4@gmail.com>
Signed-off-by: Vasant Hegde <a6d753843573f7bfed5075c1e875b0be8007a0ab@linux.vnet.ibm.com>

open-power/skiboot,qemu/skiboot,qemu/skiboot,legoater/skiboot,legoater/skiboot,qemu/skiboot,qemu/skiboot,open-power/skiboot,legoater/skiboot,shenki/skiboot,qemu/skiboot,shenki/skiboot,open-power/skiboot,shenki/skiboot,legoater/skiboot,open-power/skiboot,shenki/skiboot,open-power/skiboot,shenki/skiboot,legoater/skiboot