[U-Boot] Omap3 fix compiler warnings

This patch is against the arm/next branch.

This fixes OMAP3 boards building warning

cpu.c: In function 'cleanup_before_linux': cpu.c:64: warning: implicit declaration of function 'v7_flush_dcache_all' cpu.c:64: warning: implicit declaration of function 'get_device_type

Now OMAP3 has clean a build in MAKEALL.

Compile tested with MAKEALL and runtested on Zoom1.

Tom