Docs: Add SSDT-UNC.dsl to resolve X99 issues with UNC, thx @RemB

Changelog.md

@@ -9,6 +9,7 @@ OpenCore Changelog
 - Fixed memory array handle assignment on empty slots
 - Fixed CPUID patching on certain versions of macOS 10.4.10 and 10.4.11
 - Fixed incorrect core/thread counts on Pentium M processors
+- Added `SSDT-UNC.dsl` ACPI sample to resolve X99 issues, thx @RemB
 
 #### v0.6.2
 - Updated builtin firmware versions for SMBIOS and the rest

Docs/AcpiSamples/SSDT-UNC.dsl

+/*
+ * Discovered on X99-series.
+ * These platforms have uncore PCI bridges for 4 CPU sockets
+ * present in ACPI despite having none physically.
+ *
+ * Under normal conditions these are disabled depending on
+ * CPU presence in the socket via Processor Bit Mask (PRBM),
+ * but on X99 this code is unused or broken as such bridges
+ * simply do not exist. We fix that by writing 0 to PRBM.
+ *
+ * Doing so is important as starting with macOS 11 IOPCIFamily
+ * will crash as soon as it sees non-existent PCI bridges.
+ */
+
+DefinitionBlock ("", "SSDT", 2, "ACDT", "UNC", 0x00000000)
+{
+    External (_SB.UNC0, DeviceObj)
+    External (PRBM, IntObj)
+
+    Scope (_SB.UNC0)
+    {
+        Method (_INI, 0, NotSerialized)
+        {
+            PRBM = 0
+        }
+    }
+}