Documentation/ABI: Add new attribute for mlxreg-io sysfs interfaces

The systems of type MSN21xx, MSN201x have a slight difference from the
default reset cause bits description, it uses reset_hotswap_or_halt
instead of reset_hotswap_or_wd. New attribute is documented.
Signed-off-by: Vadim Pasternak <vadimp@mellanox.com>
Signed-off-by: Darren Hart (VMware) <dvhart@infradead.org>

Documentation/ABI/stable/sysfs-driver-mlxreg-io

@@ -57,6 +57,7 @@ Description:	These files allow asserting system power cycling, switching
 What:		/sys/devices/platform/mlxplat/mlxreg-io/hwmon/hwmon*/
 							reset_aux_pwr_or_ref
 							reset_asic_thermal
+							reset_hotswap_or_halt
 							reset_hotswap_or_wd
 							reset_fw_reset
 							reset_long_pb
@@ -67,8 +68,8 @@ Date:		June 2018
 KernelVersion:	4.19
 Contact:	Vadim Pasternak <vadimpmellanox.com>
 Description:	These files show the system reset cause, as following: power
-		auxiliary outage or power refresh, ASIC thermal shutdown,
-		hotswap or watchdog, firmware reset, long press power button,
+		auxiliary outage or power refresh, ASIC thermal shutdown, halt,
+		hotswap, watchdog, firmware reset, long press power button,
 		short press power button, software reset. Value 1 in file means
 		this is reset cause, 0 - otherwise. Only one of the above
 		causes could be 1 at the same time, representing only last