Marvell/Drivers: XenonDxe: Remove SdMmcPciHcDxe files

This patch is a preparation step for introducing new version
of the XenonDxe driver, which removes copied files from
the MdeModulePkg driver. In order not to break the compilation,
disable building XenonDxe for the one commit.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Marcin Wojtas <mw@semihalf.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>