x86/microcode/AMD: Convert CPU equivalence table variable into a struct

Convert the CPU equivalence table into a proper struct in preparation
for tracking also the size of this table.

 [ bp: Have functions deal with struct equiv_cpu_table pointers only. Rediff. ]

Signed-off-by: Maciej S. Szmigiero <mail@maciej.szmigiero.name>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: x86@kernel.org
Link: https://lkml.kernel.org/r/20181107170218.7596-15-bp@alien8.de