OMAP: hwmod: Rename hwmod name for the MPU

In the lastest OMAP4 hwmod data file, the _hwmod was removed
in order to save some memory space and because it does not
bring a lot.

The same cleanup will be have to done for other hwmods in
OMAP2 & 3 data files.

Signed-off-by: Benoit Cousson <b-cousson@ti.com>
Signed-off-by: Paul Walmsley <paul@pwsan.com>
Cc: Rajendra Nayak <rnayak@ti.com>