hwrng: Kconfig - modify default state for atmel-rng driver

In order to prevent building the Atmel hw_random driver for each and every
configuration, add a "default" Kconfig state in relation with
CONFIG_ARCH_AT91.

Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Reviewed-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

drivers/char/hw_random/Kconfig

@@ -63,7 +63,7 @@ config HW_RANDOM_AMD
 config HW_RANDOM_ATMEL
 	tristate "Atmel Random Number Generator support"
 	depends on HW_RANDOM && ARCH_AT91SAM9G45
-	default HW_RANDOM
+	default (HW_RANDOM && ARCH_AT91)
 	---help---
 	  This driver provides kernel-side support for the Random Number
 	  Generator hardware found on Atmel AT91 devices.