crypto: arm - ignore generated SHA2 assembly files

These files are generated since commits f2f770d7 (crypto: arm/sha256 - Add
optimized SHA-256/224, 2015-04-03) and c80ae7ca

 (crypto: arm/sha512 -
accelerated SHA-512 using ARM generic ASM and NEON, 2015-05-08).

Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>