crypto: arm/sha1-neon - add support for building in Thumb2 mode

The ARMv7 NEON module is explicitly built in ARM mode, which is not
supported by the Thumb2 kernel. So remove the explicit override, and
leave it up to the build environment to decide whether the core SHA1
routines are assembled as ARM or as Thumb2 code.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>