target/i386: Add a couple of feature bits in 8000_0008_EBX

target/i386: Add a couple of feature bits in 8000_0008_EBX

Add the following feature bits.

amd-psfd : Predictive Store Forwarding Disable:
           PSF is a hardware-based micro-architectural optimization
           designed to improve the performance of code execution by
           predicting address dependencies between loads and stores.
           While SSBD (Speculative Store Bypass Disable) disables both
           PSF and speculative store bypass, PSFD only disables PSF.
           PSFD may be desirable for the software which is concerned
           with the speculative behavior of PSF but desires a smaller
           performance impact than setting SSBD.
	   Depends on the following kernel commit:
           b73a54321ad8 ("KVM: x86: Expose Predictive Store Forwarding Disable")

stibp-always-on :
           Single Thread Indirect Branch Prediction mode has enhanced
           performance and may be left always on.

The documentation for the features are available in the links below.
a. Processor Programming Reference (PPR) for AMD Family 19h Model 01h,
   Revision B1 Processors
b. SECURITY ANALYSIS OF AMD PREDICTIVE STORE FORWARDING

Signed-off-by: Babu Moger <babu.moger@amd.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Link: https://www.amd.com/system/files/documents/security-analysis-predictive-store-forwarding.pdf
Link: https://www.amd.com/system/files/TechDocs/55898_B1_pub_0.50.zip
Message-Id: <20230504205313.225073-4-babu.moger@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>