x86/cpufeatures: Make AVX-VNNI depend on AVX

The 'noxsave' boot option disables support for AVX, but support for the
AVX-VNNI feature was still declared on CPUs that support it.  Fix this.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Link: https://lore.kernel.org/r/20250220060124.89622-1-ebiggers@kernel.org