mmc: remove imxmmc driver

This driver is broken since 2.6.31 when the traditional i.MX1
support was removed.

In theory the i.MX1 mmc controller can be supported by the mxcmmc
driver which basically is the same hardware. However, the i.MX1
controller has severe bugs which made several workarounds necessary which
resulted in a different driver structure. At that time it seemed easier
to write a second driver to support hardware without bugs.

As noone cared for the i.MX1 driver for a long time and it does
not compile, remove it.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Chris Ball <cjb@laptop.org>