omap: Enable PM_RUNTIME in defconfigs to avoid USB compile errors

While waiting for the related USB patch, fix compile by enabling
it in the defconfigs. As discussed at:

http://thread.gmane.org/gmane.linux.usb.general/27432/focus=4460



Otherwise we'll get errors like:

drivers/usb/core/hcd.c:1892: error: 'pm_wq' undeclared (first use in this function)
drivers/usb/core/hcd.c:1892: error: (Each undeclared identifier is reported only once
drivers/usb/core/hcd.c:1892: error: for each function it appears in.)

Signed-off-by: Tony Lindgren <tony@atomide.com>