crypto: atmel-sha204a - provide the otp content

Set up sysfs for the Atmel SHA204a. Provide the content of the otp zone as
an attribute field on the sysfs entry. Thereby make sure that if the chip
is locked, not connected or trouble with the i2c bus, the sysfs device is
not set up. This is mostly already handled in atmel-i2c.

Signed-off-by: Lothar Rubusch <l.rubusch@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>