CorebootPayloadPkg/FbGop: Produces correct PixelsPerScanLine

CorebootPayloadPkg/FbGop: Produces correct PixelsPerScanLine

According to UEFI Spec, EFI_GRAPHICS_OUTPUT_PROTOCOL.Mode->Info->
PixelsPerScanLine may contain padding pixel elements outside the area
covered by HorizontalResolution for performance reasons or due to hardware
restrictions. CorebootPayloadPkg's FbGop driver doesn't follow this
requirement, and produces PixelsPerScanLine simply as
HorizontalResolution. This needs to be fixed to reflect the real length
of a framebuffer scanline.

Cc: Maurice Ma <maurice.ma@intel.com>
Cc: Prince Agyeman <prince.agyeman@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Benjamin You <benjamin.you@intel.com>
Reviewed-by: Ruiyu Ni <ruiyu.ni@intel.com>