MLK-17750: drm/imx: ldb: Fix build on imx6/7

This code is enabled in upstream imx_v6_v7_defconfig but fails to build
because of sc api calls. Fix this by adding ifdef checks to pixel_link
code.

Check for CONFIG_HAVE_IMX8_SOC becuase it is selected by both 8qm and
8qx.

These calls are already guarded at runtime with checks for devtype
pixel_link_valid_quirks so the empty ifdefed functions will never get
called anyway.

Signed-off-by: Leonard Crestez <leonard.crestez@nxp.com>

It might make sense to add a dedicated config option for SC api
like CONFIG_HAVE_IMX_SCU, right now drivers/soc/imx/sc is guarded by
CONFIG_ARCH_FSL_IMX8QM which means you can't build 8qxp separately.