ARM: imx: imx7d requires anatop

Like i.MX6, the i.MX7 code calls into the anatop driver, which fails
if that is disabled:

arch/arm/mach-imx/built-in.o: In function `imx7d_init_machine':
arch/arm/mach-imx/mach-imx7d.c:24: undefined reference to `imx_anatop_init'
arch/arm/mach-imx/built-in.o: In function `imx7d_init_irq':
arch/arm/mach-imx/mach-imx7d.c:29: undefined reference to `imx_init_revision_from_anatop'

This patch ensures that for an imx7-only build, we still get anatop
built-in, matching what we do for imx6. We also need to select
HAVE_IMX_MMDC, as that is needed by the anatop code.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>