hwrng: pasemi - Migrate to managed API

Use devm_ioremap and devm_hwrng_register instead of ioremap and
hwrng_register. This removes unregistering and error handling code.

Changes in v2:
Remove hardcoded resource size in ioremap, use resource struct obtained
by calling platform_get_resource.

Removing hardcoded resource size was suggested by LABBE Corentin.

CC: Darren Stevens <darren@stevens-zone.net>

Suggested-by: LABBE Corentin <clabbe.montjoie@gmail.com>
Signed-off-by: PrasannaKumar Muralidharan <prasannatsmkumar@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>