drm/bridge: imx: turn imx8{qm,qxp}-ldb into single-object modules

With the previous fix, these modules are built from a single C file.

Rename the source files so they match the module names.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Liu Ying <victor.liu@nxp.com>
Signed-off-by: Robert Foss <rfoss@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230605120021.1774711-2-masahiroy@kernel.org

drivers/gpu/drm/bridge/imx/Makefile

 obj-$(CONFIG_DRM_IMX_LDB_HELPER) += imx-ldb-helper.o
-imx8qm-ldb-objs := imx8qm-ldb-drv.o
 obj-$(CONFIG_DRM_IMX8QM_LDB) += imx8qm-ldb.o
-
-imx8qxp-ldb-objs := imx8qxp-ldb-drv.o
 obj-$(CONFIG_DRM_IMX8QXP_LDB) += imx8qxp-ldb.o
-
 obj-$(CONFIG_DRM_IMX8QXP_PIXEL_COMBINER) += imx8qxp-pixel-combiner.o
 obj-$(CONFIG_DRM_IMX8QXP_PIXEL_LINK) += imx8qxp-pixel-link.o
 obj-$(CONFIG_DRM_IMX8QXP_PIXEL_LINK_TO_DPI) += imx8qxp-pxl2dpi.o