ARMV7: Fix build for non-OMAP3 boards

Commit c3d3a541 uses CONFIG_ARMV7 to determine whether to call the
v7_flush_cache_all function.  This breaks the build for all non-OMAP3
boards (like Panda and OMAP4430SDP) since there is only a v7_flush_cache_all
implementation for OMAP3.

This patch uses CONFIG_OMAP3XXX instead of CONFIG_ARMV7 so that only boards
with a v7_flush_cache_all will make the call.

Tested on Beagle, Overo, Panda, and OMAP4430SDP

Signed-off-by: Steve Sakoman <steve.sakoman@linaro.org>
Signed-off-by: Sandeep Paulraj <s-paulraj@ti.com>