arm64: proton-pack: Report Spectre-BHB vulnerabilities as part of Spectre-v2

commit dee435be76f4117410bbd90573a881fd33488f37 upstream.

Speculation effect against some high-performance processors can
make use of branch history to influence future speculation as part of
a spectre-v2. This is not mitigated by CSV2 meaning CPUs that
previously reported 'Not affected' are now moderately mitigated by CSV2.

Update the value in /sys/devices/system/cpu/vulnerabilities/spectre_v2
to show the state of the BHB mitigation.

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
[ code move to cpu_errata.c for backport ]
Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Git-commit: 7b012f65
Git-repo: https://android.googlesource.com/kernel/common/


Change-Id: I7dc0fc8e5d198c1d9d7b3d8227a93b43d746c97a
Signed-off-by: Kishor Krishna Bhat <quic_kishkris@quicinc.com>