remoteproc: pru: add support for configuring GPMUX based on client setup

The GPMUX config value for a PRU device can now be configured by client
by specifying it in the device node ti,pruss-gp-mux-sel.

Signed-off-by: Tero Kristo <t-kristo@ti.com>
Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: MD Danish Anwar <danishanwar@ti.com>
Link: https://lore.kernel.org/r/20230802064925.1895750-1-danishanwar@ti.com


Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>