coresight: Rename of_coresight to coresight-platform

Rename the firmware handling file to a more generic
name, in preparation for adding ACPI support. Right now
we only support DT and we have all the platform handling
code in of_coresight.c. Let us rename the file to
coresight-platform.c in order to keep the platform handling
in a single place for DT and the upcoming ACPI support.

Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>