BACKPORT: KVM: arm64: Advertise KVM UID to guests via SMCCC

We can advertise ourselves to guests as KVM and provide a basic features
bitmap for discoverability of future hypervisor services.

BUG=b:230005239
BUG=b:230582047
TEST=tast run arc.Boot.vm

Backport-notes:
Fix to change all 'val =' to 'val[0] =' in kvm_hvc_call_handler()
since other upstream spectre mitigations have been backported already.

Cc: Marc Zyngier <maz@kernel.org>
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Jianyong Wu <jianyong.wu@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Masami Hiramatsu <mhiramat@google.com>
Link: https://lore.kernel.org/r/20201209060932.212364-3-jianyong.wu@arm.com
(cherry picked from commit 923961a7)
Change-Id: I6c96fe6a09becbc395aed548af6044bbbd1a3199
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/3848979


Commit-Queue: Suleiman Souhlal <suleiman@chromium.org>
Reviewed-by: Suleiman Souhlal <suleiman@chromium.org>