ARM: OMAP4/5: Add generic board detection hook

Many TI EVMs have capability to store relevant board information
such as DDR description in EEPROM. Further many pad configuration
variations can occur as part of revision changes in the platform.
In-order to support these at runtime, we for a board detection hook
which is available for override from board files that may desire to do
so.

NOTE: All TI EVMs are capable of detecting board information based on
early clocks that are configured. However, in case of additional needs
this can be achieved within the override logic from within the board
file.

Signed-off-by: Steve Kipisz <s-kipisz2@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Lokesh Vutla <lokeshvutla@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>