x86/vtx: Corrections to BDF93 errata workaround

x86/vtx: Corrections to BDF93 errata workaround

At the time of fixing c/s 20f1976b44, no obvious errata had been published,
and BDF14 looked like the most obvious candidate.  Subsequently, BDF93 has
been published and it is obviously this.

The erratum states that LER_TO_LIP is the only affected MSR.  The provisional
fix in Xen adjusted LER_FROM_LIP, but this is not correct.  The FROM MSRs are
intended to have TSX metadata, and for steppings with TSX enabled, it will
corrupt the value the guest sees, while for parts with TSX disabled, it is
redundant with FIXUP_TSX.  Drop the LER_FROM_LIP adjustment.

Replace BDF14 references with BDF93, drop the redundant 'bdw_erratum_' prefix,
and use an Intel vendor check, as other vendors implement VT-x.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Release-acked-by: Juergen Gross <jgross@suse.com>