remove mmu_cache_lock as it protects a section which is already
protected by mmu_lock.

in addition, wrap mmu cache invalidate calls in hl_vm_ctx_fini with
mmu_lock.
Signed-off-by: NOhad Sharabi <osharabi@habana.ai>
Reviewed-by: NOded Gabbay <ogabbay@kernel.org>
Signed-off-by: NOded Gabbay <ogabbay@kernel.org>