ArmPlatformPkg: Reserving framebuffer at build

ArmPlatformPkg: Reserving framebuffer at build

Currently framebuffer memory is either reserved in special VRAM or
dynamically allocated using boot services memory allocation functions.
When allocated using boot services calls the memory has to be allocated
as EfiBootServicesData. Unfortunately failures have been seen with this
case.  There is also an unfortunate lack of control on the placement of
the framebuffer.

This change introduces two PCDs, PcdArmLcdFrameBufferBase and
PcdArmLcdFrameBufferSize which enable build time reservation of the
framebuffer, avoiding the need to allocate dynamically. This allows
the framebuffer to appear as "I/O memory" outside of the normal RAM
map, which is similar to the "VRAM" case.

This change has no impact on current code, only enables the option
of build time reservation of framebuffers.

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>