ARM: DRA7: Move emif settings to board specific files

The newer versions of DRA7 boards has EEPROM populated with DDR
size specified in it. Moving DRA7 specific emif related settings
to board files so that emif settings can be identified based on EEPROM.

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