[S390] ap: Use high-resolution timer for polling

The ap poll mechanism is converted to use a high-resolution timer for
polling. This allows more specific polling. With this a new sysfs
attribute is introduced to specify the polling rate in nanoseconds.

Signed-off-by: Felix Beck <felix.beck@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>