usb: host: Add ability to build new Broadcom STB USB drivers

Add the build system changes needed to get the Broadcom STB XHCI,
EHCI and OHCI functionality working. The OHCI support does not
require anything unique to Broadcom so the standard ohci-platform
driver is being used. Also update MAINTAINERS.

Signed-off-by: Al Cooper <alcooperx@gmail.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Link: https://lore.kernel.org/r/20200512150019.25903-6-alcooperx@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>