staging: dwc2: platform device wrapper

FIXME: write a patch description. Describe the changes I made.

Signed-off-by: Paul Zimmerman <paulz@synopsys.com>
[swarren: many changes, described above]
Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>
HACK: enable DWC2 OTG on RPi

Turn on USB power first in U-Boot:

// msg with 2 parameters, up to 2 responses
setenv prop-2-2 'mw.l 0x00001000 0x00000020 ; mw.l 0x00001004 0x00000000 ; mw.l 0x00001008 \$tag ; mw.l 0x0000100c 0x00000008 ; mw.l 0x00001010 0x00000008 ; mw.l 0x00001014 \$p1 ; mw.l 0x00001018 \$p2 ; mw.l 0x0000101c 0x00000000 ; md.l 0x1000 8'

// send msg, read/dump response
setenv send-rec 'mw 0x2000b8a0 0x00001008 ; md 0x2000b880 1 ; md.l 0x00001000 8'

// set power, devid==p1 (3==USB), state,wait==p2 (3==ON/WAIT)
setenv tag 0x28001 ; setenv p1 3 ; setenv p2 3; run prop-2-2 ; run send-rec

Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>