Do not build Intel content restriction modules

These kernel modules are only usable if the GPU is attached to dom0.
However, dom0 never has the userspace programs needed to use these
modules, so the modules are unused.  Worse, if mei_hdcp *was* used, it
would allow external displays (which are not trusted) to communicate
with the (closed-source and often out-of-date) CSME firmware, which is
even more privileged than dom0.

config-qubes

@@ -158,6 +158,22 @@ CONFIG_INTEL_PMC_CORE=m
 
 # CONFIG_XEN_VIRTIO is not set
 
+## INTEL_MEI_HDCP and DRM_AMD_DC_PDCP are for High-bandwidth Digital Content
+## Protection, and INTEL_MEI_PXP is for Protected Xe Path.  Since the Intel CSME
+## and AMD Secure Processor must never be passed through to a VM, these are only
+## usable if there is an Intel or AMD GPU attached to dom0.  However, dom0 does
+## not include any programs that can use these modules, so the modules are
+## unused.  Worse, if HDCP *was* used, it would, it would allow external
+## displays (which are not trusted) to communicate with the (closed-source and
+## often out-of-date) CSME or Secure Processor firmware, which is even more
+## privileged than dom0.
+
+# CONFIG_DRM_AMD_DC_HDCP is not set
+# CONFIG_INTEL_MEI_HDCP is not set
+
+## PXP serves no purpose without userspace tools Qubes OS does not have.
+# CONFIG_INTEL_MEI_PXP is not set
+
 ################################################################################
 ## TODO: from diff to old config