EDAC/amd64: Add context struct

Define an address translation context struct. This will hold values that
will be passed between multiple functions.

Save return address, Node ID, and the Instance ID number to start.
Currently, the UMC number is used as the Instance ID, but future DF
versions may use another value.

Also include a "tmp" field to use when reading registers. This is to
avoid having to define a temporary variable in multiple functions.

Signed-off-by: Yazen Ghannam <yazen.ghannam@amd.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211028175728.121452-5-yazen.ghannam@amd.com