x86/speculation: Use ARCH_CAPABILITIES to skip L1D flush on vmentry

x86/speculation: Use ARCH_CAPABILITIES to skip L1D flush on vmentry

Bit 3 of ARCH_CAPABILITIES tells a hypervisor that L1D flush on vmentry is
not needed.  Add a new value to enum vmx_l1d_flush_state, which is used
either if there is no L1TF bug at all, or if bit 3 is set in ARCH_CAPABILITIES.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Orabug: 28220674
CVE: CVE-2018-3620

(cherry picked from commit 8e0b2b916662e09dd4d09e5271cdf214c6b80e62)

Signed-off-by: Mihai Carabas <mihai.carabas@oracle.com>
Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Conflicts:
	arch/x86/include/asm/msr-index.h
	arch/x86/kernel/cpu/bugs.c
msr-index.h: different location
bugs.c: different filename