remoteproc/keystone: add support for Keystone 2 Galileo SOCs

Add support to the keystone remoteproc driver for managing the
DSP present in the Keystone 2 Galileo (K2G) SoC. The K2G SoC has
a Power Management Micro Controller (PMMC) that manages the
individual device's power, clock and reset functionalities.

The keystone remoteproc driver already uses standard frameworks
for reset and clock control, so it doesn't require any significant
modifications other than a new compatible suitable for K2G DSP.

The binding document is also updated to reflect the modified
property values used by the K2G DSP node as compared to the
values used by existing Keystone 2 DSPs.

NOTE:
The enhancement to use common pm_runtime framework for all Keystone
2 SoCs is left for a future time. The redundata clock API usage for
K2G does not impact any functionality, but is still required for
other K2 SoCs.

Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Andrew F. Davis <afd@ti.com>