Change NNAPI time from steady_clock to boot_clock -- hal

Previously, the NNAPI used std::chrono::steady_clock to represent and
measure timings. However, steady_clock does not count while the system
is suspended. Instead, boot_clock is monotonic like steady_clock but
does include the time when the system is suspended.

This change also indicates that services may convert from
std::chrono::steady_clock::time_point to
android::base::boot_clock::time_point in the HIDL 1.3 NN HAL.

Bug: 183118340
Test: mma
Test: VtsHalNeuralnetworksV1_3TargetTest
Test: VtsHalNeuralnetworksTargetTest
Test: presubmit
Change-Id: I5a7d039a31d9ce98602a301387ec99635f279f42