ti_armv7_keystone2: Define scratch space in SRAM

Scratch space can be used for features such as board detection. Define
an area within SRAM that can be used for this purpose.

[rogerq@ti.com] Rename EEPROM macro

Signed-off-by: Franklin S Cooper Jr <fcooper@ti.com>
Signed-off-by: Roger Quadros <rogerq@ti.com>