phy: Add a driver for the ATH79 USB phy

The ATH79 USB phy is very simple, it only have a reset. On some SoC a
second reset is used to force the phy in suspend mode regardless of the
USB controller status.

This driver is added to the qualcom directory as atheros is now part
of qualcom and newer SoC of this familly are marketed under the
qualcom name.

Signed-off-by: Alban Bedel <albeu@free.fr>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>