ARM: OMAP4+: vcores: Remove duplicated code

There is no reason to duplicate code for DRA7xx platforms as there
can be Rail grouping. The maximum voltage detection algorithm can still
be run on other platforms with no Rail grouping and does not harm as
it gives the same result.

Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>