s390/zcrypt: enable s390 hwrng to seed kernel entropy

Set the 'quality' property in the zcrypt rng device structure to enable the
zcrypt hwrng device to take part in the kernel entropy seeding process.
A module parameter named hwrng_seed will be introduced to disable the
participation. By default this parameter is set to 1 (enabled).

Signed-off-by: Ingo Tuchscherer <ingo.tuchscherer@de.ibm.com>
Signed-off-by: Harald Freudenberger <freude@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>