sunxi: Drop legacy usb_phy.c

Allwinner PHY USB code is now part of generic-phy framework,
so drop existing legacy handling like arch/arm/mach-sunxi.c
and related code areas.

Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Acked-by: Jun Nie <jun.nie@linaro.org>