ARM: OMAP4+: PRCM MPU: Move function prototypes to common header for re-use

OMAP5 reuses OMAP4 MPU PRCM IP block which lets us re-use functions.
So move the function prototypes from prcm_mpu44xx.h to prcm_mpu_44xx_54xx.h
header. The suggestion came from Paul Walmsley as part of the
OMAP5 data file review.

This is preparatory  patch to add OMAP5 MPU PRCM data file.

Cc: Paul Walmsley <paul@pwsan.com>
Acked-by: Rajendra Nayak <rnayak@ti.com>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Signed-off-by: Paul Walmsley <paul@pwsan.com>