FROMLIST: coresight: ETM: Add support for ARM Cortex-A73

Add ARM Cortex A-73 ETM PIDs to the known ETM ips. While at it
also add description of the CPU to which the ETM belongs, to make
it easier to identify the ETM devices.

Change-Id: I031859b31e99d8b1fcd41474d4d339b685ef0ef4
Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>