ARM: k2g: Define embedded_dtb_select for runtime DTB selection in U-boot

ARM: k2g: Define embedded_dtb_select for runtime DTB selection in U-boot

For K2G, runtime DTB selection utilizes the embedded_dtb_select function.
Therefore, define the function which will perform a EEPROM read and then
retries selecting the correct dtb now that it can detect which board its
on. For other Keystone devices use an empty function since they will still
use the embedded FIT functionality but their FIT will only contain a single
dtb.

Most production K2G boards do not have their EEPROM programmed. Therefore,
perform a test to verify a K2G GP is currently being used and if it is then
set the values normally set by a EEPROM read.

Signed-off-by: Franklin S Cooper Jr <fcooper@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>