crypto: atmel - refine Kconfig dependencies

With the new authenc support, we get a harmless Kconfig warning:

warning: (CRYPTO_DEV_ATMEL_AUTHENC) selects CRYPTO_DEV_ATMEL_SHA which has unmet direct dependencies (CRYPTO && CRYPTO_HW && ARCH_AT91)

The problem is that each of the options has slightly different dependencies,
although they all seem to want the same thing: allow building for real AT91
targets that actually have the hardware, and possibly for compile testing.

This makes all four options consistent: instead of depending on a particular
dmaengine implementation, we depend on the ARM platform, CONFIG_COMPILE_TEST
as an alternative when that is turned off. This makes the 'select' statements
work correctly.

Fixes: 89a82ef8

 ("crypto: atmel-authenc - add support to authenc(hmac(shaX), Y(aes)) modes")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>