KVM: arm64: Add templates for BHB mitigation sequences

KVM writes the Spectre-v2 mitigation template at the beginning of each
vector when a CPU requires a specific sequence to run.
Because the template is copied, it can not be modified by the alternatives
at runtime. As the KVM template code is intertwined with the bp-hardening
callbacks all templates must have a bp-hardening callback.
Add templates for calling ARCH_WORKAROUND_3  and one for each value of K
in the brancy-loop. Identify these sequences by a new parameter
template_start, and add a copy of install_bp_hardening_cb() that is able to
install them.

Change-Id: I3dbb2d1e06663cbf39b1d212547ac64d569fd72e
Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Git-commit: a68912a3
Git-repo: https://android.googlesource.com/kernel/common/


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