x86/cpufeatures: Add X86_FEATURE_SGX_EUPDATESVN feature flag

x86/cpufeatures: Add X86_FEATURE_SGX_EUPDATESVN feature flag

Add a flag indicating whenever ENCLS[EUPDATESVN] SGX instruction is
supported. This will be used by SGX driver to perform CPU SVN updates.

Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Reviewed-by: Kai Huang <kai.huang@intel.com>
Reviewed-by: Dave Hansen <dave.hansen@linux.intel.com>
Tested-by: Nataliia Bondarevska <bondarn@google.com>