x86/common: Stamp out the stepping madness

The whole MMIO/RETBLEED enumeration went overboard on steppings. Get
rid of all that and simply use ANY.

If a future stepping of these models would not be affected, it had
better set the relevant ARCH_CAP_$FOO_NO bit in
IA32_ARCH_CAPABILITIES.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>