arm_ffa: introduce sandbox FF-A support

Emulate Secure World's FF-A ABIs and allow testing U-Boot FF-A support

Features of the sandbox FF-A support:

- Introduce an FF-A emulator
- Introduce an FF-A device driver for FF-A comms with emulated Secure World
- Provides test methods allowing to read the status of the inspected ABIs

The sandbox FF-A emulator supports only 64-bit direct messaging.

Signed-off-by: Abdellatif El Khlifi <abdellatif.elkhlifi@arm.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Cc: Tom Rini <trini@konsulko.com>
Cc: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Cc: Jens Wiklander <jens.wiklander@linaro.org>
Cc: Heinrich Schuchardt <xypron.glpk@gmx.de>

include/dm/uclass-id.h

@@ -63,6 +63,7 @@ enum uclass_id {
 	UCLASS_ETH_PHY,		/* Ethernet PHY device */
 	UCLASS_EXTCON,		/* External Connector Class */
 	UCLASS_FFA,		/* Arm Firmware Framework for Armv8-A */
+	UCLASS_FFA_EMUL,		/* sandbox FF-A device emulator */
 	UCLASS_FIRMWARE,	/* Firmware */
 	UCLASS_FPGA,		/* FPGA device */
 	UCLASS_FUZZING_ENGINE,	/* Fuzzing engine */