ANDROID: KVM: arm64: Add clock support in the nVHE hyp

By default, the arm64 host kernel is using the arch timer as a source
for sched_clock. Conveniently, EL2 has access to that same counter,
allowing to generate clock values that are synchronized.

The clock needs nonetheless to be setup with the same slope values as
the kernel. Introducing at the same time trace_clock() which is expected
to be later configured by the hypervisor tracing.

Bug: 229972309
Change-Id: Icc560124e6b0879c8085b2eeb0b6123da907a7ae
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>