x86/speculation/mmio: Reuse SRBDS mitigation for SBDS

commit a992b8a4682f119ae035a01b40d4d0665c4a2875 upstream

The Shared Buffers Data Sampling (SBDS) variant of Processor MMIO Stale
Data vulnerabilities may expose RDRAND, RDSEED and SGX EGETKEY data.
Mitigation for this is added by a microcode update.

As some of the implications of SBDS are similar to SRBDS, SRBDS mitigation
infrastructure can be leveraged by SBDS. Set X86_BUG_SRBDS and use SRBDS
mitigation.

Mitigation is enabled by default; use srbds=off to opt-out. Mitigation
status can be checked from below file:

  /sys/devices/system/cpu/vulnerabilities/srbds

Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
[cascardo: adjust for processor model names]
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>