plat-k3: drivers: Add secure proxy driver for communication with System Controller

Secure Proxy is a communication scheme in Texas Instrument's devices
intended to provide an unique communication pa

plat-k3: drivers: Add secure proxy driver for communication with System Controller

Secure Proxy is a communication scheme in Texas Instrument's devices
intended to provide an unique communication path from various processors
in the System on Chip(SoC) to a central System Controller.

Secure Proxy instance exposes "threads" or "proxies" which is
primary representation of "a" communication channel. Each thread is
preconfigured by System controller configuration based on SoC usage
requirements. Secure proxy by itself represents a single "queue" of
communication but allows the proxies to be independently operated.

For communication with TISCI, Secure Proxy driver is required in OP-TEE.

NOTE: Secure proxy configuration is only done by System Controller,
hence these are assumed to be pre-configured instances.

Provide the driver support for Secure Proxy and thread instances.

Tested on AM65x.

See AM65x Technical Reference Manual (SPRUID7E, April 2018)
for further details: https://www.ti.com/lit/ug/spruid7e/spruid7e.pdf

Signed-off-by: Manorit Chawdhry <m-chawdhry@ti.com>
Acked-by: Andrew Davis <afd@ti.com>
Acked-by: Jerome Forissier <jerome.forissier@linaro.org>

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