arm: cache: add missing dummy functions for when dcache disabled

arm: cache: add missing dummy functions for when dcache disabled

Adds missing flush_dcache_range and invalidate_dcache_range dummy
(empty) placeholder functions to the #else portion of the #ifndef
CONFIG_SYS_DCACHE_OFF, where full implementations of these functions
are defined.

Signed-off-by: Daniel Allred <d-allred@ti.com>
Signed-off-by: Andreas Dannenberg <dannenberg@ti.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>