MPC83xx, MPC85xx: compile stub cache function

MPC83xx, MPC85xx: compile stub cache function

An empty flush_dcache_range() was added into MPC83xx and MPC85xx to
work with drivers shared with other architecture.  However, it is
compiled only if USB is set, but it is required for other drivers
(FSL_ESDHC), too.

Signed-off-by: Stefano Babic <sbabic@denx.de>
CC: Andy Fleming <afleming@gmail.com>
CC: Dirk Behme <dirk.behme@de.bosch.com>
CC: Marek Vasut <marex@denx.de>
CC: Wolfgang Denk <wd@denx.de>
Added MPC83xx version.

Signed-off-by: Wolfgang Denk <wd@denx.de>