MdeModulePkg/AcpiTableDxe: condense whitespace around FADT.{DSDT,X_DSDT}

This patch incurs no functional changes, it just removes some whitespace,
and also makes sure we always assign

  AcpiTableInstance->Fadt3->Dsdt

first, and

  AcpiTableInstance->Fadt3->XDsdt

second. The goal is to separate the syntactic changes from the functional
changes implemented by the next patch.

Cc: Al Stone <ahs3@redhat.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Feng Tian <feng.tian@intel.com>
Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Leo Duran <leo.duran@amd.com>
Cc: Michael Tsirkin <mtsirkin@redhat.com>
Cc: Phil Dennis-Jordan <phil@philjordan.eu>
Cc: Star Zeng <star.zeng@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Feng Tian <feng.tian@intel.com>
Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>
Reviewed-by: Star Zeng <star.zeng@intel.com>