hwrng: nomadik - add ARM_AMBA dependency

Compile-testing this driver is only possible when the AMBA bus driver is
available in the kernel:

x86_64-linux-ld: drivers/char/hw_random/nomadik-rng.o: in function `nmk_rng_remove':
nomadik-rng.c:(.text+0x67): undefined reference to `amba_release_regions'
x86_64-linux-ld: drivers/char/hw_random/nomadik-rng.o: in function `nmk_rng_probe':
nomadik-rng.c:(.text+0xee): undefined reference to `amba_request_regions'
x86_64-linux-ld: nomadik-rng.c:(.text+0x18d): undefined reference to `amba_release_regions'

The was previously implied by the 'depends on ARCH_NOMADIK', but needs to be
specified for the COMPILE_TEST case.

Fixes: d5e93b3374e4 ("hwrng: Kconfig - Add helper dependency on COMPILE_TEST")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>