DRA7: add ABB setup for MPU voltage domain

Patch adds modification to shared omap5 abb_setup() function, and
proper registers definitions needed for ABB setup sequence. ABB is
initialized for MPU voltage domain at OPP_NOM.

Signed-off-by: Nishanth Menon <nm@ti.com>
Reviewed-by: Tom Rini <trini@ti.com>