mmc: sh_mobile_sdhi: remove obsolete include file

A few SH boards include the file but don't make use of it (no named
interrupts). The SDHI code removed support for this feature as well.
So, drop the references and ultimately remove the unneeded file.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Acked-by: Rich Felker <dalias@libc.org>
Acked-by: Yoshinori Sato <ysato@users.sourceforge.jp>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>