i386/cpu: Rename AMD_ENC_ASSOC to X86_ENC_ASSOC

i386/cpu: Rename AMD_ENC_ASSOC to X86_ENC_ASSOC

Rename AMD_ENC_ASSOC to X86_ENC_ASSOC since Intel also uses the same
rules.

While there are some slight differences between the rules in AMD APM
v4.07 no.40332 and Intel. But considerring the needs of current QEMU,
generally they are consistent and current AMD_ENC_ASSOC can be applied
for Intel CPUs..

Tested-by: Yi Lai <yi1.lai@intel.com>
Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
Link: https://lore.kernel.org/r/20250711102143.1622339-10-zhao1.liu@intel.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>