ARM: shmobile: sh7372: Remove ZBOOT MMC/SDHI support

Remove the sh7372 implementation and the shared ZBOOT MMC
and SDHI support code from the compressed ARM boot loader.

With this in place it is no longer possible to boot any
self-contained kernel for sh7372 directly from Mask ROM
via SDHI and MMCIF hardware.

Signed-off-by: Magnus Damm <damm+renesas@opensource.se>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>