x86/intel_rdt: Turn off most RDT features on Skylake

Errata list is included in this document:
https://www.intel.com/content/dam/www/public/us/en/documents/specification-updates/6th-gen-x-series-spec-update.pdf
with more details in:
https://www.intel.com/content/www/us/en/processors/xeon/scalable/xeon-scalable-spec-update.html

But the tl;dr summary (using tags from first of the documents) is:
SKZ4 MBM does not accurately track write bandwidth
SKZ17 CMT counters may not count accurately
SKZ18 CAT may not restrict cacheline allocation under certain conditions
SKZ19 MBM counters may undercount

Disable all these features on Skylake models. Users who understand the
errata may re-enable using boot command line options.

Signed-off-by: Tony Luck <[e-mail]>
Cc: Fenghua" <[e-mail]>
Cc: Ravi V" <[e-mail]>
Cc: "Peter Zijlstra" <[e-mail]>
Cc: "Stephane Eranian" <[e-mail]>
Cc: "Andi Kleen" <[e-mail]>
Cc: "David Carrillo-Cisneros" <[e-mail]>
Cc: Vikas Shivappa <[e-mail]>
Link: http://lkml.kernel.org/r/3[e-mail]
Signed-off-by: Thomas Gleixner <[e-mail]>

arch/x86/kernel/cpu/intel_rdt.c

···
 		if (!rdt_options[RDT_FLAG_L3_CAT].force_off)
 			cache_alloc_hsw_probe();
 		break;
+	case INTEL_FAM6_SKYLAKE_X:
+		if (boot_cpu_data.x86_mask <= 4)
+			set_rdt_options("!cmt,!mbmtotal,!mbmlocal,!l3cat");
 	}
 }