ARM: OMAP2+: Limit omap_read/write usage to legacy USB drivers

Drivers should no longer use omap_read/write functions
but instead use ioremap + read/write functions.

As some USB legacy code is still shared between omap1 and
omap2420, let's limit the omap_read/write to plat/usb.h.

Note that the long term fix is to update the drivers to
use ioremap and read/write functions. That can now be
done as a separate patch series that is limited to the
USB drivers.

Also make sure the legacy omap1-keypad.c driver builds
if selected for 2420 based systems.

Cc: Tomi Valkeinen <tomi.valkeinen@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>
diff --git a/arch/arm/plat-omap/include/plat/keypad.h b/arch/arm/plat-omap/include/plat/keypad.h
index 793ce9d..a6b21ed 100644
--- a/arch/arm/plat-omap/include/plat/keypad.h
+++ b/arch/arm/plat-omap/include/plat/keypad.h
@@ -12,6 +12,8 @@
 
 #ifndef CONFIG_ARCH_OMAP1
 #warning Please update the board to use matrix-keypad driver
+#define omap_readw(reg)		0
+#define omap_writew(val, reg)	do {} while (0)
 #endif
 #include <linux/input/matrix_keypad.h>