OMAP4: PRM: Remove MPU internal code name and apply PRCM naming convention

The MPU subsystem was named based on internal code name (CHIRON).
This patch will remove all the occurences of the chiron name
are replace it with PRCM_MPU in order to differentiate
the MPU local PRCM to the global one.

Remove PDA_ from PRCM_MPU registers names to stick to the global
PRM naming convention.

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