board: ti: AM57xx: Add detection logic for AM57xx-evm

board: ti: AM57xx: Add detection logic for AM57xx-evm

Current AM57xx evm supports both BeagleBoard-X15
(http://beagleboard.org/x15) and AM57xx EVM
(http://www.ti.com/tool/tmdxevm5728).

The AM572x EValuation Module(EVM) provides an affordable platform to
quickly start evaluation of Sitara. ARM Cortex-A15 AM57x Processors
(AM5728, AM5726, AM5718, AM5716) and accelerate development for HMI,
machine vision, networking, medical imaging and many other industrial
applications. This EVM is based on the same BeagleBoard-X15 Chassis
and adds mPCIe, mSATA, LCD, touchscreen, Camera, push button and TI's
wlink8 offering.

Since the EEPROM contents are compatible between the BeagleBoard-X15 and
the AM57xx-evm, we add support for the detection logic to enable
support for various user programmable scripting capability.

NOTE: U-boot configuration is currently a superset of AM57xx evm and
BeagleBoard-X15 and no additional configuration tweaking is needed.

This change also sets up the stage for future support of TI AM57xx EVMs
to the same base bootloader build.

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