ARM: OMAP2: Move plat/menelaus.h to linux/mfd/menelaus.h

We can move menelaus.h to live with other mfd headers to
get it out of plat for ARM common zImage support.

Acked-by: Samuel Ortiz <sameo@linux.intel.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>