musb-new: am35x backend driver

musb-new: am35x backend driver

Backend driver for MUSB OTG controllers found on TI AM35x.

It seems that on AM35X interrupt status registers can be updated
_before_ core registers. As we don't use true interrupts in U-Boot
and poll interrupt status registers instead this can result in
interrupt handler being called with non-updated core registers.
This confuses the code and result in hanged transfers.
Add a small delay in am35x_interrupt as a workaround.

Signed-off-by: Ilya Yanok <ilya.yanok@cogentembedded.com>