MdeModulePkg/AcpiTableDxe: Not make FADT.{DSDT,X_DSDT} mutual exclusion

MdeModulePkg/AcpiTableDxe: Not make FADT.{DSDT,X_DSDT} mutual exclusion

198a46d768fb90d2f9b16e26451b4814e7469eaf improved the DSDT and X_DSDT
fields mutual exclusion by checking FADT revision, but that breaks
some OS that has assumption to only consume X_DSDT field even the
DSDT address is < 4G.

To have better compatibility, this patch is to update the code to not
make FADT.{DSDT,X_DSDT} mutual exclusion, but always set both DSDT and
X_DSDT fields in the FADT when the DSDT address is < 4G.

Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Jeff Fan <jeff.fan@intel.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Star Zeng <star.zeng@intel.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Tested-by: Jeff Fan <jeff.fan@intel.com>