crypto: x86/aesni-gcm - make 'struct aesni_gcm_tfm_s' static const

Add missing static keywords to fix the following sparse warnings:

    arch/x86/crypto/aesni-intel_glue.c:197:24: warning: symbol 'aesni_gcm_tfm_sse' was not declared. Should it be static?
    arch/x86/crypto/aesni-intel_glue.c:246:24: warning: symbol 'aesni_gcm_tfm_avx_gen2' was not declared. Should it be static?
    arch/x86/crypto/aesni-intel_glue.c:291:24: warning: symbol 'aesni_gcm_tfm_avx_gen4' was not declared. Should it be static?

I also made the affected structures 'const', and adjusted the
indentation in the struct definition to not be insane.

Cc: Dave Watson <davejwatson@fb.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>