ANDROID: KVM: arm64: allow trace file to be open for read

Userspace tools might want to open trace files for read (e.g. to check
if they have access to the tracing interface), so instead of returning
-EPERM we make this a no-op.

Bug: 428904926
Test: presubmit
Change-Id: I32b1b6db543f462dc986578cebd803d8312fe6bb
Signed-off-by: Nikita Ioffe <ioffe@google.com>