usb: musb: Fix transmission of bigger buffers

usb: musb: Fix transmission of bigger buffers

If udc_endpoint_write() was called with bigger payload which does not fit
into one USB packet it is needed to transmit payload in more USB packets.
First packet is transmitted by udc_endpoint_write() call itself and other
packets are put into waiting queue.

Implement function musb_peri_tx() which checks if endpoints are ready for
transmit and continue transmission of waiting queue.

This patch fixes sending big output from printenv command over usbtty
serial console.

Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Lukasz Majewski <lukma@denx.de>
Acked-by: Pavel Machek <pavel@ucw.cz>>