x86/boot: Adjust MSR_ARCH_CAPS handling for the Host policy

We are about to move MSR_ARCH_CAPS into featureset, but the order of
operations (copy raw policy, then copy x86_capabilitiles[] in) will end up
clobbering the ARCH_CAPS value.

Some toolstacks use this information to handle TSX compatibility across the
CPUs and microcode versions where support was removed.

To avoid this transient breakage, read from raw_cpu_policy rather than
modifying it in place.  This logic will be removed entirely in due course.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
(cherry picked from commit 43912f8dbb)

xen/arch/x86/cpu-policy.c

@@ -411,7 +411,7 @@ static void __init calculate_host_policy(void)
     p->platform_info.cpuid_faulting = cpu_has_cpuid_faulting;
 
     /* Temporary, until we have known_features[] for feature bits in MSRs. */
-    p->arch_caps.raw &=
+    p->arch_caps.raw = raw_cpu_policy.arch_caps.raw &
         (ARCH_CAPS_RDCL_NO | ARCH_CAPS_IBRS_ALL | ARCH_CAPS_RSBA |
          ARCH_CAPS_SKIP_L1DFL | ARCH_CAPS_SSB_NO | ARCH_CAPS_MDS_NO |
          ARCH_CAPS_IF_PSCHANGE_MC_NO | ARCH_CAPS_TSX_CTRL | ARCH_CAPS_TAA_NO |