usb: musb: Drop old unused am35x glue layer

The am35x glue layer is no longer in use and can be dropped. There are no
longer any SoCs passing platform data for it as they are booting using
devicetree.

In general, the am35x SoCs are similar to am335x and ti81xx and can
use the musb_dsps glue layer as long as there is a proper phy driver
available.

Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Link: https://lore.kernel.org/r/20221125085506.38127-1-tony@atomide.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>