ARM: OMAP2: Use a consistent AM33XX SoC option description

Fix the option description to match the other TI SoCs.
This is just a cosmetic change.

Signed-off-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Reviewed-by: Javier Martinez Canillas <javier@dowhile0.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>