mmc: convert drivers/mmc/host/* to use module_platform_driver()

This patch converts the drivers in drivers/mmc/host/* to use the
module_platform_driver() macro which makes the code smaller and a bit
simpler.

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Acked-by: "Michał Mirosław" <mirq-linux@rere.qmqm.pl>
Acked-by: David Brown <davidb@codeaurora.org>
Acked-by: Viresh Kumar <viresh.kumar@st.com>
Acked-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Acked-by: Sascha Hauer <s.hauer@pengutronix.de>
Acked-by: Wolfram Sang <w.sang@pengutronix.de>
Acked-by: Anton Vorontsov <cbouatmailru@gmail.com>
Signed-off-by: Chris Ball <cjb@laptop.org>