mmc: sdhci: Stop advertising the driver in dmesg

mmc: sdhci: Stop advertising the driver in dmesg

As much as we have grown used to seeing this message on
every kernel boot, it does not add any technical value.

Drop all messages from sdhci_drv_init(), and drop the
module_init() and module_exit() calls as well since they
now become empty.

The modules becomes a pure library module, meaning it will
get pulled in by modprobe() when the symbols inside it
are needed, or compiled in if any users are compiled in.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>