Update SRAM start & size for am33xx SoC's.

Note: cpu_is_34xx() is true for am33xx also. Doing
cpu_is_am33xx() check after cpu_is_34xx() will not
achieve what we want due to the above reason.
Hence cpu_is_am33xx() is done before cpu_is_34xx()
Signed-off-by: Vaibhav Bedia <vaibhav.bedia@ti.com>
Signed-off-by: Afzal Mohammed <afzal@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>