MdeModulePkg/MdeModulePkg/dsc: move DxeDebugSupportDxe to x86 only section

MdeModulePkg/MdeModulePkg/dsc: move DxeDebugSupportDxe to x86 only section

MdeModulePkg/Universal/DebugSupportDxe/DebugSupportDxe.inf does not
build for AARCH64 since it does not provide the needed PlDebugSupport.h
header. So move the module to a x86 only section.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Jian J Wang <jian.j.wang@intel.com>
Reviewed-by: Star Zeng <star.zeng@intel.com>.