thunderbolt: Introduce tb_switch_next_cap()

This is similar to tb_port_next_cap() but instead allows walking
capability list of a switch (router). Convert tb_switch_find_cap() and
tb_switch_find_vse_cap() to use this as well.

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/drivers/thunderbolt/tb.h b/drivers/thunderbolt/tb.h
index 54e8fad..a1d5de5 100644
--- a/drivers/thunderbolt/tb.h
+++ b/drivers/thunderbolt/tb.h
@@ -822,6 +822,7 @@ int tb_port_get_link_speed(struct tb_port *port);
 
 int tb_switch_find_vse_cap(struct tb_switch *sw, enum tb_switch_vse_cap vsec);
 int tb_switch_find_cap(struct tb_switch *sw, enum tb_switch_cap cap);
+int tb_switch_next_cap(struct tb_switch *sw, unsigned int offset);
 int tb_port_find_cap(struct tb_port *port, enum tb_port_cap cap);
 int tb_port_next_cap(struct tb_port *port, unsigned int offset);
 bool tb_port_is_enabled(struct tb_port *port);