iommu/amd: Do not clear event/ppr log buffer when snp is enabled

iommu/amd: Do not clear event/ppr log buffer when snp is enabled

Current code clears event log and ppr log entry after processing it due
to hardware errata ([1]  erratum #732, #733). We do not have hardware
issue on SNP enabled system.

When SNP is enabled, the event logs, PPR log and completion wait buffer
are read-only to the host (see SNP FW ABI spec [2]). Clearing those entry
will result in a kernel #PF for an RMP violation. Hence do not clear
event and ppr log entry after processing it.

[1] http://developer.amd.com/wordpress/media/2012/10/48931_15h_Mod_10h-1Fh_Rev_Guide.pdf
[2] https://www.amd.com/system/files/TechDocs/56860.pdf

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Vasant Hegde <vasant.hegde@amd.com>
Reviewed-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Link: https://lore.kernel.org/r/20230117044038.5728-1-vasant.hegde@amd.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>