thunderbolt: Move usb4_switch_wait_for_bit() to switch.c

Currently usb4_switch_wait_for_bit() used only in usb4.c Moving to
switch.c to call it from other files. Also change the prefix to "tb_"
to follow to the naming convention.

Signed-off-by: Gil Fine <gil.fine@intel.com>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>