ArmPkg: Introduce SCMI protocol

ArmPkg: Introduce SCMI protocol

This change introduces a new SCMI protocol driver for
Arm systems. The driver currently supports only clock
and performance management protocols. Other protocols
will be added as and when needed.

Clock management protocol is used to configure various clocks
available on the platform e.g. HDLCD clock on the Juno platforms.

Whereas performance management protocol allows adjustment
of various performance domains. Currently this is used to evaluate
performance of the Juno platform.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Girish Pathak <girish.pathak@arm.com>
Signed-off-by: Evan Lloyd <evan.lloyd@arm.com>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>