am335x_evm: Define CONFIG_SYS_CACHELINE_SIZE

drivers/usb/gadget/composite.c requires that this is defined early.

Signed-off-by: Pantelis Antoniou <panto@antoniou-consulting.com>
Signed-off-by: Tom Rini <trini@ti.com>
Acked-by: Tom Rini <trini@ti.com>