UefiPayloadPkg: Support variable size MMCONF space
The default size is still 256MiB, but will be overwritten by
UefiPayloadPkg with the real MMCONF size.
e.g.: On embedded AMD platforms the MMCONF window size is usually
only 64MiB.
Fixes crash on platforms not exposing 256 buses.
Tested on:
* AMD Stoney Ridge
Signed-off-by: Patrick Rudolph <patrick.rudolph@9elements.com> Signed-off-by: Marcello Sylvester Bauer <marcello.bauer@9elements.com> Cc: Patrick Rudolph <patrick.rudolph@9elements.com> Cc: Christian Walter <christian.walter@9elements.com> Cc: Maurice Ma <maurice.ma@intel.com> Cc: Nate DeSimone <nathaniel.l.desimone@intel.com> Cc: Benjamin You <benjamin.you@intel.com> Reviewed-by: Guo Dong <guo.dong@intel.com>