x86/amd_node: Use defines for SMN register offsets

There are more than one SMN index/data pair available for software use.
The register offsets are different, but the protocol is the same.

Use defines for the SMN offset values and allow the index/data offsets
to be passed to the read/write helper function.

This eases code reuse with other SMN users in the kernel.

Signed-off-by: Yazen Ghannam <yazen.ghannam@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Link: https://lore.kernel.org/r/20241206161210.163701-14-yazen.ghannam@amd.com