[Pal/Linux-SGX] pal-sgx-sign: rename avx3 to avx512

Consistency fixup.
This introduces incompatible change. Manifests need to be updated
to use enable_avx512 instead of enable_avx3.

Pal/src/host/Linux-SGX/signer/pal-sgx-sign

@@ -140,7 +140,7 @@ def get_enclave_attributes(manifest):
     sgx_xfrms = {
         'XFRM_LEGACY'         : struct.pack("<Q", SGX_XFRM_LEGACY),
         'XFRM_AVX'            : struct.pack("<Q", SGX_XFRM_AVX),
-        'XFRM_AVX3'           : struct.pack("<Q", SGX_XFRM_AVX512),
+        'XFRM_AVX512'         : struct.pack("<Q", SGX_XFRM_AVX512),
         'XFRM_MPX'            : struct.pack("<Q", SGX_XFRM_MPX),
     }
 
@@ -159,7 +159,7 @@ def get_enclave_attributes(manifest):
 
     manifest_options = {
         'debug'          : 'FLAG_DEBUG',
-        'enable_avx3'    : 'XFRM_AVX3',
+        'enable_avx512'  : 'XFRM_AVX512',
         'enable_mpx'     : 'XFRM_MPX',
         'support_exinfo' : 'MISC_EXINFO',
     }