arm64: KVM: Preserve RES1 bits in SCTLR_EL2

arm64: KVM: Preserve RES1 bits in SCTLR_EL2

commit d68c1f7fd1b7148dab5fe658321d511998969f2d upstream.

__do_hyp_init has the rather bad habit of ignoring RES1 bits and
writing them back as zero. On a v8.0-8.2 CPU, this doesn't do anything
bad, but may end-up being pretty nasty on future revisions of the
architecture.

Let's preserve those bits so that we don't have to fix this later on.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <cdall@linaro.org>
[bwh: Backported to 3.16:
 - s/ELx/EL2/
 - Adjust filename, context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>