remoteproc: pru: Add support for various PRU cores on K3 AM62x SoCs

The K3 AM62x family of SoC has one PRUSS-M instance and it has two
Programmable Real-Time Units (PRU0 and PRU1). This does not support
Industrial Communications Subsystem features like Ethernet.

Enhance the existing PRU remoteproc driver to support the PRU cores
by using specific compatibles. The initial names for the firmware
images for each PRU core are retrieved from DT nodes, and can be adjusted
through sysfs if required.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Link: https://lore.kernel.org/r/20220602101920.12504-4-kishon@ti.com
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>