Revert "x86/cpu: Add a steppings field to struct x86_cpu_id"

This reverts commit 749ec6b4.

This is commit e9d71445 upstream. A proper
backport will be done. This will make it easier to check for parts affected
by Retbleed, which require X86_MATCH_VENDOR_FAM_MODEL.

Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>