usb: chipidea: big-endian support

Convert between big-endian and little-endian format when accessing the usb
controller structures which are little-endian by specification.
Fix cases where the little-endian memory layout is taken for granted.
The patch doesn't have any effect on the already supported little-endian
architectures.

Signed-off-by: Svetoslav Neykov <svetoslav@neykov.name>
[Alex: minor cosmetic fixes]
Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>