ArmPlatformPkg: introduce LcdHwLib library class

ArmPlatformPkg: introduce LcdHwLib library class

Add the declaration and include file for the new LcdHwLib library class,
which will allow us to abstract away from platform  variations in the
LCD graphics output driver.

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>
[ardb: add NULL implementation as well and add it to ArmPlatformPkg.dsc]
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>