s390/hiperdispatch: Add hiperdispatch debug attributes

Add two attributes for debug purposes. They can be found under;
/sys/devices/system/cpu/hiperdispatch/
* hd_stime_threshold : allows user to adjust steal time threshold
* hd_delay_factor : allows user to adjust delay factor of hiperdispatch
                    work (after topology updates, delayed work is
                    always delayed extra by this factor)

hd_stime_threshold can have values between 0-100 as it represents a
percentage value.
hd_delay_factor can have values greater than 1. It is multiplied with
the default delay to achieve a longer interval, pushing back the next
hiperdispatch adjustment after a topology update.

Ex:
if delay interval is 250ms and the delay factor is 4;
delayed interval is now 1000ms(1sec). After each capacity adjustment
or topology change, work has a delayed interval of 1 sec for one
interval.

Acked-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Mete Durlu <meted@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>