OvmfPkg: Rename IS_ALIGNED macros to avoid name collisions

This patch is a preparation for the patches that follow. The
subsequent patches will introduce and integrate new alignment-related
macros, which collide with existing definitions in OvmfPkg.
Temporarily rename them to avoid build failure, till they can be
substituted with the new, shared definitions.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Michael D Kinney <michael.d.kinney@intel.com>
Reviewed-by: Jiewen Yao <Jiewen.yao@intel.com>
Acked-by: Tom Lendacky <thomas.lendacky@amd.com>