ArmPlatformPkg: Redefine LcdPlatformGetTimings function
The LcdPlatformGetTimings interface function takes similar sets of
multiple parameters for horizontal and vertical timings which can be
aggregated in a common data type. This change defines a structure
SCAN_TIMINGS for this which can be used to describe both horizontal and
vertical scan timings, and accordingly redefines the
LcdPlatformGetTiming interface, greatly reducing the amount of data
passed about.