x86/ucode/amd: Overhaul the equivalent cpu table handling completely

x86/ucode/amd: Overhaul the equivalent cpu table handling completely

We currently copy the entire equivalency table, and the single correct
microcode.  This is not safe to heterogeneous scenarios, and as Xen doesn't
support such situations to begin with, can be used to simplify things further.

The CPUID.1.EAX => processor_rev_id mapping is fixed for an individual part.
We can cache the single appropriate entry on first discovery, and forgo
duplicating the entire table.

Alter install_equiv_cpu_table() to be scan_equiv_cpu_table() which is
responsible for checking the equivalency table and caching appropriate
details.  It now has a check for finding a different mapping (which indicates
that one of the tables we've seen is definitely wrong).

A return value of -ESRCH is now used to signify "everything fine, but nothing
applicable for the current CPU", which is used to select the
container_fast_forward() path.

Drop the printk(), as each applicable error path in scan_equiv_cpu_table()
already prints diagnostics.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>