USB: fsl_udc_core: fix build breakage when building for ARM arch

Commit 09ba0def (USB: fsl_udc_core: prepare for SoCs with
BE registers and descriptors) introduced build breakage
on ARM arch. Fix it by setting accessors using a static
inline function which is a nop when compiling the driver
for ARM arch.

Commit 2ea6698d (USB: fsl_udc_core: support device mode of
MPC5121E DR USB Controller) caused another breakage on ARM
by using flush_dcache_range(). Don't use it, convert to the
DMA API usage instead. USB2.0CV Halt Endpoint Test succeeds
on PPC. Tested both on ARM i.MX31 and mpc5121 PPC, also with
CONFIG_DMA_API_DEBUG enabled.

Signed-off-by: Anatolij Gustschin <agust@denx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>