hwrandom / exynos / PM: Use CONFIG_PM in #ifdef

CONFIG_PM is defined as the alternative of CONFIG_PM_RUNTIME and
CONFIG_PM_SLEEP, so it can be used instead of that.

Besides, after commit b2b49ccb (PM: Kconfig: Set PM_RUNTIME if
PM_SLEEP is selected) PM_RUNTIME is always set if PM is set, so
using the alternative isn't even necessary.

Use CONFIG_PM instead of it in drivers/char/hw_random/exynos-rng.c.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Herbert Xu <herbert@gondor.apana.org.au>